SB    TL   fl33 

LTURAL 

;TERIOLOQY 

3ELL  &  HASTINGS 


3 


Arie. 


in  Lib. 


LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 


Class 


BIOLOGY 

LIBRARY 

6 


AGRICULTURAL 

BACTERIOLOGY 


BY 

H.  L.  RUSSELL 

DEAN  OP  THE  COLLEGE  OF  AGRICULTURE 
UNIVERSITY  OF  WISCONSIN 

AND 

E.  G.  HASTINGS 

ASSOCIATE  PROFESSOR  OF  AGRICULTURAL  BACTERIOLOGY 
UNIVERSITY  OF  WISCONSIN 


OF   THE 

UNIVERSITY 

OF 


MADISON,  WISCONSIN 
H.  L.  RUSSELL 

1909 


BIOLOGY 

LIBRARY 

G 


Afffe.  Dept. 

COPYRIGHT,  1909 

BY 
H.  L.  RUSSELL  AND  E.  G.  HASTINGS. 


STATE  JOyRN"AL  PRINTING  COMPANY 

PaiNTERS  AND  STEREOTYPERS 

MADISON,  Wis. 


FOREWORD. 


No  single  line  of  discovery  has  exerted  a  more  pro- 
found influence  on  the  scientific  thought  of  the  last  few 
decades  than  has  the  development  of  bacteriology.  The 
researches  of  Pasteur,  Koch,  and  their  successors,  opened 
a  field  of  inquiry  that  has  not  only  revolutionized  all  of 
the  biological  sciences,  but  also  the  applied  lines  of 
thought.  Medicine  was  the  first  of  these  sciences  to  re- 
ceive the  impetus  from  such  discoveries,  but  it  is  no  less 
true  that  they  exert  an  equally  profound  effect  on  agri- 
cultural sciences.  Too  long  has  agriculture  been  consid- 
ered simply  an  art — a  vocation  which  one  had  to  learn 
wholly  in  the  school  of  experience,  but  the  serious  student 
of  farm  life  finds  it  necessary  to  understand  the  phenom- 
ena of  the  plant  and  animal  world  and  to  combat  or  util- 
ize successfully  the  activities  of  various  microscopic  or- 
ganisms. It  is  therefore  essential,  even  in  a  practical 
course,  that  this  important  subject  be  properly  consid- 
ered. The  text  here  presented  deals  with  the  subject 
briefly,  but  it  is  designed  to  give  a  comprehensive  treat- 
ment of  the  different  relations  which  the  bacteria  bear 
to  problems  of  farm  life.  At  best,  it  can  only  serve  to 
stimulate  the  interest  of  the  student  to  pursue  this  sub- 
ject more  in  detail  as  opportunity  permits. 


201935 


OF  TH€ 

UNIVERSITY 

OF 


CONTENTS 


SECTION  I 

GENERAL  BACTERIOLOGY 

CHAPTER    I    Structure,  Growth,  and  Distribution  of  Bacteria.       1 
II     Artificial  Cultivation  of  Bacteria 15 

SECTION  II 
RELATION  OP  BACTERIA  TO  MILK  AND  OTHER  DAIRY  PRODUCTS 

CHAPTEK  III  Contamination  of  Milk 22 

IV  Preservation  of  Milk 44 

V  Fermentations  of  Milk 53 

VI  Relation  of  Bacteria  to  Butter 65 

VII  Relation  of  Bacteria  to  Cheese 73 

VIII  Relation  of  Bacteria  to  Market  Milk 82 

SECTION  III 
RELATION  OF  BACTERIA  TO  DISEASE 

•CHAPTER  IX    Transmissible  Diseases 92 

X    Anthrax,  Black  Leg,  Hemorrhagic  Septicaemia, 

and  Corn  Stalk  Disease 98 

XI    Tuberculosis . 110 

XII    Glanders  and  Tetanus 127 

XIII  Rabies , 134 

XIV  Actinomycosis,  Garget,  Cow  Pox,  and  Contagi- 

ous Garget 142 

XV    Diseases  of  Hogs 151 

XVI    Diseases  of  Fowls 157 

XVII    Miscellaneous  Diseases 161 

XVIII     Disinfection..  .   165 


VI 


Contents. 


SECTION  IV 
RELATION  OF  BACTERIA  TO  SOILS 

CHAPTER  XIX     Relation  of  Bacteria  to  Fertility 171 

XX    Effect  of  Bacteria  on  Minerals  of  the  Soil 183 

XXI  Ammonification,  Nitrification,  and  Denitrifi- 

cation 186 

XXII    Fixation  of  Nitrogen 195 

XXIII  Bacteria  in  Manures ^  . . .  207 

XXIV  Water  Supply  and  Sewage  Disposal 214 

SECTION  V 

FOOD  PRESERVATION  AND  DISEASES  OF  PLANTS 

CHAPTER  XXV    Preservation  of  Foods 225 

XXVI    Diseases  of  Plants 235 


SECTION  1. 
GENERAL  BACTERIOLOGY. 

CHAPTER  I. 
STRUCTURE,  GROWTH  AND  DISTRIBUTION. 

Nature  of  the  bacteria.  The  bacteria  belong  to  the 
group  of  plants  known  as  fungi.  The  fungus  plants  do 
not  contain  the  green  coloring  matter  found  in  ordinary 
plants.  They  live  on  dead  or  living  animal  or  vegetable 
matter.  Many  of  the  fungi  are  well  known  to  the 
farmer  and  are  of  great  economic  importance  causing, 
as  they  do,  such  plant  diseases  as  the  rusts,  smuts  and 
mildews.  Other  examples  of  fungi  are  the  various 
kinds  of  molds,  toadstools  and  mushrooms.  These  are 
more  familiar  as  they  are  large  enough  to  be  seen  by  the 
unaided  eye,  while  many  other  kinds  of  fungi  and  es- 
pecially the  bacteria  are  unfamiliar  objects  because  by 
the  unaided  eye  an  individual  plant  can  not  be  seen. 
When  massed  together  in  large  numbers  they  become 
visible  but  such  groupings  are  rarely  found  in  nature. 

While  the  bacteria,  themselves,  are  not  familiar  ob- 
jects the  effect  they  produce  is  very  evident  in  the  sour- 
ing of  milk,  the  spoiling  of  meat  and  eggs,  the  produc- 
tion of  diseases  in  plants  and  animals,  and  in  many 
other  ways  which  are  not  so  readily  recognized. 

Knowledge  relating  to  the  bacteria  has  nearly  all 
been  gained  within  the  last  thirty  years  although  the 
bacteria  were  first  seen  by  a  Dutch  lens-maker,  Antoni 
van  Leeuwenhoek,  in  1675.  For  nearly  two  hundred 
years  after  they  were  first  discovered  but  little  of  im- 
portance was  learned  concerning  them. 


2  Agricultural  Bacteriology. 

Structure  of  bacteria.  Plants  and  animals  are  made 
up  of  cells  which  are  tiny  masses  of  semi-liquid  matter 
surrounded  by  a  membrane,  the  cell  wall.  Many  kinds 
of  cells  are  found  in  each  individual  higher  plant 
or  animal.  The  sum  total  of  the  activities  of  all  the 
cells  constitutes  the  life  of  the  individual.  Bacteria  are 
made  of  cells  the  same  as  other  living  things,  but  in- 
stead of  a  number  of  cells  being  required  to  form  an 
individual,  each  cell  is  a  complete  organism  in  itself, 
capable  of  carrying  on  all  the  processes  necessary  for 
the  continuance  of  its  life.  The  single  cell  can  breathe, 
take  in  food,  live,  and  reproduce  itself.  Thus  while  the 
bacteria  are  very  simple  as  to  their  structure,  they  per- 
form all  the  necessary  functions  of  a  living  organism. 


A  B  C  ;. 

FIG.  1. — FORMS  OF  BACTERIA. 
A,  coccus;  B,  bacillus;  C,   spirillum.      (After  Novy.) 

Forms  of  bacteria.  Where  the  individual  is  reduced 
to  the  limits  of  a  single  cell,  it  is  evident  that  not  much 
variation  in  form  is  possible.  While  slight  variations 
in  size  and  shape  are  to  be  noted,  nearly  all  the  bacteria 
may  be  grouped  under  three  general  types.  The  ball- 
shaped  are  known  as  cocci  (singular  coccus) ;  the  rod- 
shaped  are  called  bacilli  (singular  bacillus) ;  if  the  rods 
instead  of  being  straight  are  more  or  less  curved,  they 
are  known  as  spirilla  (singular  spirillum).  The  ball- 
shaped  and  the  rod-shaped  are  by  far  the  most  abun- 
dant and  are  the  forms  of  most  interest  to  the  student  of 
agricultural  bacteriology. 


Structure,  Growth  and  Distribution.  3 

Size  of  bacteria.  All  of  the  bacteria  are  so  small  they 
n  not  be  seen  by  the  unaided  eye.  In  fact  their  min- 
uteness is  such  as  to  render  difficult  any  adequate  con- 
ception of  their  size.  In  a  single  teaspoonful  of  sour 
cream  ready  for  the  churn,  there  are  often  1,500.000,000 
bacteria.  The  teaspoonful  of  cream  is  not  more 
crowded  than  is  our  world  with  the  1,500,000,000  peo- 
ple living  on  its  surface.  In  the  drop  of  cream  each 
organism  is  living  its  own  life  and  doing  a  certain 
amount  of  work  as  is  each  person  on  the  surface  of  the 
globe. 

The  different  kinds  of  bacteria  vary  considerably  in 
relative  size.  The  largest  may  be  several  hundred  times 
as  large  as  the  smallest  forms.  Even  with  the  largest, 
one  hundred  or  more  laid  side  by  side  would  not  equal 
in  thickness  an  ordinary  sheet  of  paper. 

Manner  of  reproduction.  Most  of  the  ordinary  plants 
increase  in  number  by  forming  seeds.  The  seed  ger- 
minates and  grows  into  a  plant  which  may  produce 
thousands  of  seeds  similar  to  the  one  planted.  Many 
kinds  of  fungus  plants  reproduce  by  the  formation  of 
spores,  which  in  some  ways  are  analogous  to  the  seeds 
of  the  higher  plants.  The  cloud  of  smoke  from  the  ripe 
puffball  is  made  up  of  its  tiny  spores.  The  ripe  smut 
on  the  corn  owes  its  black  color  to  the  multitude  of 
spores  it  contains. 

In  their  manner  of  reproduction  the  bacteria  are  to 
be  compared  to  the  individual  cell  of  the  higher  plant 
or  animal  rather  than  to  the  entire  plant.  The  germi 
nating  corn  plant  is  made  up  of  a  number  of  cells. 
These  divide  each  into  two,  these  two  cells  again  divide 
to  form  four  cells  and  so  on,  the  plant,  meanwhile,  in- 


4  Agricultural  Bacteriology. 

creasing  in  size.  The  bacteria  increase  in  number  in  a 
similar  way,  each  cell  dividing  into  two  at  each  division. 
The  mother  cell  disappears  and  two  daughter  cells  are 


FIG.  2. — DIVISION  OF  BACTERIA. 

The  bacteria  increase  in  numbers  through  the  divi- 
sion of  each  cell  into  two  cells.      (After  Novy.) 

formed,  which  in  turn  soon  become  mother  cells  and 
thus  the  process  is  repeated. 

Arrangement  of  cells.  Each  kind  of  plant  can  be  rec- 
ognized because  the  cells  forming  it  are  arranged  in  a 
certain  definite  way,  different  from  the  arrangement  of 
the  cells  in  all  other  plants.  The  arrangement  of  the 
cells  of  those  kinds  of  bacteria  that  cling  together  after 
the  cell  has  divided  often  enables  the  experienced  bac- 


A  B  c 

FIG,.  3. — ARRANGEMENT  OF  BACTERIA. 

A,  streptococci;  B,  sarcina;  C,  staphylococci.     (After 

Novy.) 

teriologist  to  recognize  different  types.  The  cells  may 
be  arranged  in  long  or  short  chains.  Such  aggregates 
of  cocci  are  known  as  streptococci ;  clusters  of  cocci  re- 
sembling bunches  of  grapes  are  called  staphylococci. 
Still  other  forms  of  cocci  divide  in  such  a  manner  as 


Structure,  Growth  and  Distribution.  5 

to  form  packets  of  cells  resembling  a  bale  of  binder 
twine  (sarcina),  while  many  forms  show  no  regularity 
in  the  grouping  of  the  cells.  But  few  of  the  bacilli  and 
spirilla  show  a  characteristic  grouping  of  the  cells. 

Spores  of  bacteria.  The  seeds  of  plants  are  not  so 
easily  injured  by  heat,  cold,  or  drying  as  are  the  grow- 
ing plants  which  bear  them.  The  seeds  thus  carry  over 
the  plant  from  one  growing  season  to  the  next.  Many 
kinds  of  bacteria  form  within  the  cell  a  tiny  structure, 
called  a  spore,  which  is  much  more  resistant  than  the 
vegetating  cell,  and  hence,  in  this  respect  is  comparable 


FIG.  4. — SPOKE  FORMATION  AND  GERMINATION. 
Figures  on  upper  line  show  various  stages  of  spore 
development.     Lower  left  hand   figure  represents 
the   cell   issuing   from   the   spore   case. 

to  the  seeds  of  ordinary  plants.  The  spores  are,  how- 
ever, much  more  resistant  than  the  seeds  of  any  of  the 
higher  plants.  Boiling  for  hours  will  not  kill  some 
kinds  of  bacterial  spores.  They  can  be  dried  for  years 
and  still  grow  quickly  when  placed  in  a  favorable  food- 
material.  Thus,  the  bacteria  forming  spores  are  able 
to  withstand  unfavorable  environmental  conditions. 

The  spores  are  unlike  seeds  in  that  spore  formation 
is  not  to  be  considered  as  a  manner  of  increasing  in 


6  Agricultural  Bacteriology. 

numbers  since  one  cell  forms  but  a  single  spore,  and  c 
germination  this  spore  grows  into  a  single  cell.  N< 
all  bacteria  form  spores,  a  very  fortunate  circumstan< 
as  will  be  seen  later.  The  resistant  spores  often  gr\ 
to  the  dairyman  and  farmer  a  great  amount  of  trouble 

Movement  of  bacteria.  Plants  as  a  rule  do  not  mov 
yet  some  of  our  common  plants  can  move  their  leave 
as  the  ordinary  sensitive  plant.  Many  water  plan 
possess  organs  of  locomotion.  Certain  of  the  bacter: 
are  able  to  move  in  the  liquids  in  which  they  exis 
This  motion  is  accomplished  by  the  lashing  to  and  fi 
of  the  fine  hair-like  processes  known  as  cilia.  Tl 
movement  of  the  bacteria  is  really  very  slow  althoug: 
when  a  drop  of  a  liquid  containing  motile  bacteria 
seen  under  the  microscope,  the  bacteria  seem  to  be  mo1 
ing  rapidly  about,  for  their  motion  is  magnified  in  tl 
same  manner  as  are  the  bacteria  themselves. 

Food  supply  of  bacteria.  The  green  plant  lives  o 
certain  inorganic  substances  in  the  soil.  The  colorle? 
group  of  plants  to  which  the  bacteria  belong,  the  fung 
live  on  living  or  on  dead  animal  and  vegetable  matte 
By  far  the  majority  of  the  bacteria  find  most  favorab] 
conditions  for  growth  on  dead  organic  matter.  The 
cause  the  spoiling  of  our  food-stuffs  and  are  largely  r( 
sponsible  for  the  complete  disappearance  of  the  aninu 
and  vegetable  matter  that  reaches  the  soil.  They  ar 
thus  of  the  utmost  importance  for  without  them  th 
earth  would  soon  be  encumbered  with  the  dead  bodie 
of  plants  and  animals.  To  consume  this  organic  ma1 
ter  is  the  function  of  the  class  of  bacteria  known  as  th 
saprophytic  bacteria.  The  bacteria  that,  under  natura 
conditions,  live  only  in  the  bodies  of  living  plants  an* 


Structure,  Growth  and  Distribution.  1 

animals  are  called  parasitic  bacteria.  To  the  latter 
group  belong  those  especially  important  forms,  the  pa- 
thogenic bacteria,  which  produce  the  transmissible  dis- 
eases of  plants  and  animals.  Some  species  ordinarily 
lead  a  saprophytic  life  in  the  soil,  but  may,  if  accident 
introduces  them  into  the  bodies  of  animals,  grow  and 
produce  serious  trouble.  These  forms  are  not  to  be 
looked  upon  as  parasites  since  their  natural  habitat  is- 
not  the  body  of  a  living  animal. 

The  saprophytic  as  also  the  parasitic  bacteria  vary 
widely  as  to  the  kind  of  food  best  adapted  to  their  dif- 
ferent needs.  Some  kinds  of  parasitic  bacteria  grow 
only  in  the  body  of  man,  others  only  in  certain  animals; 
while  still  other  types  grow  in  the  bodies  of  a  large 
number  of  different  kinds  of  animals.  Some  of  the  soil 
bacteria  grow  only  on  certain  kinds  of  food  substances, 
while  others  flourish  on  the  widest  variety  of  materials. 

Condition  of  the  food.  Since  the  food  must  be  ab- 
sorbed by  the  bacterial  cell  before  it  can  be  used,  it  is 
necessary  that  it  be  in  solution.  Some  forms  of  bac- 
teria are  able  to  develop  digesting  substances,  known  as. 
enzymes,  by  means  of  which  they  render  insoluble  ma- 
terial soluble,  utilizing  the  same  in  part  as  food. 

Bacteria  can  not,  as  a  rule,  grow  well  in  acid  sub- 
stances, a  fact  which  is  widely  applied  in  the  preserva- 
tion of  human  and  animal  foods.  In  this  respect  they 
differ  from  most  of  the  fungi  which  thrive  preferably 
on  acid  rather  than  on  neutral  or  alkaline  substances. 
Jellies  and  plant  juices,  therefore,  spoil  from  mold  de- 
velopment while  blood  and  animal  products  as  broths 
and  soups  undergo  bacterial  decomposition. 

Oxygen  supply  of  bacteria.  Every  living  thing,  even 
every  living  cell  of  the  growing  plant  or  animal,  must 


8  Agricultural  Bacteriology. 

have  air,  or  rather  oxygen.  The  bacteria  are  no  excep- 
tion to  this  rule.  Many  forms  known  as  aerdbes  (liv- 
ing in  the  air)  can  grow  only  in  the  presence  of  oxygen. 
A  smaller  group  known  as  anaerobes  (living  without 
air)  grow  only  in  the  total  absence  of  free  oxygen. 
These  forms  must,  however,  have  oxygen,  but  their  only 
•available  source  is  the  combined  oxygen  which  they  se- 


FIG.  5. — PHOTOMICROGRAPH  OF  ANTHRAX  BACILLI. 

The  chain-like  arrangement  is  characteristic  of  this 
organism.  Each  member  of  the  chain  is  an  indi- 
vidual bacillus.  Magnified  1,000  diameters. 

cure  from  organic  substances  like  sugar.     An  interme- 
diate type  is  able  to  live  and  grow  under  either  condi- 
tion, i.  e.,  in  the  presence  or  absence  of  free  oxygen 
/These  are  called  facultative  anaerobes. 

Moisture  supply  of  bacteria.  No  cell  growth  of  any 
kind  can  take  place  without  moisture.  Bacterial 
changes  go  on  most  rapidly  in  the  presence  of  an  abun- 


Structure,  Growth  and  Distribution.  9 

dant  supply  of  moisture.  Foods,  such  as  meats,  fruits, 
vegetables  and  also  fodders  are  protected  from  the  ac- 
tion of  bacteria  and  molds  by  drying.  Molds  require 
much  less  moisture  for  their  growth  than  do  the  bac- 
teria. 

Temperature  for  the  growth  of  bacteria.  In  common 
with  other  forms  of  plant  life,  bacterial  growth  occurs 
throughout  a  relatively  wide  temperature  zone ;  in  fact, 
wider  than  in  the  case  of  most  other  plant  forms.  Most 
forms  of  bacteria  are  checked  in  their  growth  when  the 
temperature  approximates  40°-45°  F.  although  a  few  of 
them  thrive  near  the  freezing  point.  At  ordinary  air 
temperatures,  multiplication  of  the  cells  proceeds  apace 
as  is  shown  by  the  decomposition  of  organic  substances. 
During  hot  summer  weather,  80°-100°  F.,  decomposi- 
tion is  still  further  hastened.  If,  however,  the  tem- 
perature is  increased  much  above  the  blood  heat, 
growth  of  most  forms  is  checked.  A  temperature  of 
180°-140°  F.  actually  kills  most  of  the  vegetating  bac- 
teria. To  exceed  this  fatal  point,  known  as  the  ther- 
mal death  point,  is  the  basis  of  all  methods  of  preserva- 
tion of  foods  by  heat. 

Bate  of  growth  of  bacteria.  When  a  suitable  food  is 
available  and  temperature  conditions  are  favorable,  the 
bacteria  increase  in  numbers  very  rapidly.  A  single 
organism  will  divide,  and  the  two  daughter  cells  grow 
to  maturity,  ready  to  divide  again,  in  twenty  minutes  or 
less.  This  rate  of  growth  rarely  takes  place  under  na- 
tural conditions  and  is  never  maintained  for  any  con- 
siderable length  of  time  for  most  forms  of  life  encoun- 
ter conditions  in  nature  that  restrict  their  development. 


10  Agricultural  Bacteriology. 

Food  is  not  always  abundant,  the  temperature  may  be- 
such  as  to  limit  or  even  stop  growth.  Every  living  thing 
has  its  enemies.  These  limitations  check  bacterial  growth 
in  the  same  manner  as  all  the  higher  forms  of  life  are 
checked. 

Under  artificial  conditions  the  bacteria  may  grow 
very  rapidly  for  a  time.  For  instance,  it  has  been 
shown  that  a  single  organism  when  placed  under  the 
most  favorable  conditions  as  to  food  and  temperature 
will  increase  in  ten  hours  to  the  enormous  number  of 
1,240,000,000.  This  rapid  growth  does  not  continue, 
but,  on  the  other  hand,  goes  on  more  and  more  slowly 
and  at  last  ceases  altogether,  because  the  products 
formed  by  the  organisms]  themselves  accumulate  and 
make  further  growth  impossible.  Every  form  of  life 
living  on  plant  or  animal  matter  may  be  killed  by  its 
own  excretions  unless  they  are  removed.  The  bacteria 
are  no  exception  to  this  rule. 

Effect  of  cold  on  bacteria.  Low  temperatures  retard 
the  rate  of  growth  of  the  bacteria.  The  exact  point  at 
which  growth  ceases  varies  widely  with  different  spe- 
cies. Some  forms  as  the  organism  causing  tuberculosis 
will  not  grow  below  90°  F.  Still  others  will  grow  at 
temperatures  below  freezing  when  they  are  present  in 
a  liquid  like  brine  that  does  not  freeze.  When  the  sub- 
stance in  which  the  bacteria  are  present  becomes  solid  by 
freezing,  growth  must  cease  but  the  bacteria  are  not 
necessarily  killed.  For  example  water  bacteria  are  not 
all  killed  by  freezing  although  it  is  popularly  supposed 
that  water  purifies  itself  in  this  manner.  Even  disease- 
producing  bacteria  may  resist  this  degree  of  cold  for  a 


Sfriiclur< .  Growth  and  Distribution.  11 

number  of  months.     For  this  reason  ice  used  in  cooling 
drinking    water    should    come    only    from    uncontami- 

nated  sources. 

• 

Effect  of  heat  on  bacteria.  All  forms  of  life  are  de- 
stroyed by  high  temperatures.  The  seeds  of  the  higher 
plants  are  not  so  easily  killed  by  heat  as  are  the  plants 
themselves  and  in  the  same  way  the  spores  formed  by 
certain  of  the  bacteria  are  very  difficult  to  kill.  Some 
must  be  subjected  to  the  temperature  of  boiling  water 
(212°  F.)  for  hours  in  order  to  destroy  them. 

Two  forms  of  heat  are  used  to  destroy  bacteria,  moist 
heat,  as  steam  or  hot  water,  and  dry  heat  as  produced 
in  an  oven.  As  every  one  knows,  one  can  place  his 
hand  in  an  oven  heated  much  above  212°  F.  without  in- 
jury, but  the  same  exposure  to  steam  or  boiling  water 
would  result  in  a  serious  burn.  The  effect  on  the  bac- 
teria is  the  same.  For  this  reason  when  it  is  desired  to 
destroy  germ  life  on  or  in  any  substance,  moist  heat  is 
preferably  used  if  it  will  not  injure  the  object. 

Effect  of  light  on  bacteria.  All  the  plants  which  con- 
tain the  green  coloring  matter,  chlorophyll,  can  produce 
a  normal  growth  only  in  the  presence  of  light.  Fungi 
grow  rapidly  in  the  dark.  To  some  of  the  fungi  the 
light  is  not  especially  injurious.  The  bacteria,  espe- 
cially the  pathogenic  bacteria,  even  in  a  spore  stage, 
are  easily  killed  by  direct  sunlight.  As  previously 
stated,  the  spores  are  very  difficult  to  kill  by  heating, 
much  more  so  than  the  vegetating  cell,  but  sunlight 
kills  the  spores  of  most  forms  almost  as  quickly  as  it- 
does  the  growing  cell. 

While  the  direct  sunlight  is  very  efficient  in  destroy- 
ing both  cells  and  spores,  the  diffused  light  of  an  ordi- 


12  Agricultural  Bacteriology. 

nary  house  or  barn  has  but  little  effect.     Where  the 
"bacteria  are  covered  by  dust  or  dirt  light  has  no  effect. 

Effect  of  chemicals  on  bacteria.  Many  chemical  sub- 
stances are  poisonous  to  plants  and  animals.  When 
such  substances  exert  a  peculiarly  marked  effect  on 
germ  life  they  are  known  as  disinfectants  or  germicides. 
Corrosive  sublimate,  carbolic  acid,  and  formaldehyde 
are  the  best  known  and  strongest  disinfectants.  When 
present  in  very  small  amounts  they  do  not  kill  the  bac- 
terial cells  but  may  prevent  their  growth.  Some  chem- 
icals, even  in  strong  solutions,  are  not  poisonous  enough 
to  kill  the  bacteria  but  may  merely  check  the  growth. 
Such  are  known  as  antiseptics  or  preservatives.  All  dis- 
infectants in  a  dilute  form  have  an  antiseptic  action, 
but  not  all  antiseptics,  even  in  concentrated  solutions, 
are  disinfectants.  For  example,  lime  is  an  antiseptic, 
since  it  dissolves  in  water  to  such  an  extent  as  to  pre- 
vent all  growth  of  bacteria,  but  it  does  not  kill  many 
forms  of  bacteria.  Acids,  such  as  vinegar,  are  anti- 
septics, and  are  constantly  used  in  the  preservation  of 
human  and  animal  foods. 

Products  formed  by  bacteria.  When  the  bacteria 
grow  in  any  food-substance,  parts  of  the  same  are  con- 
mimed.  As  a  result  of  this  growth,  the  bacteria  give 
off  from  their  bodies  various  kinds  of  by-products  that 
are  very  different  from  the  original  food-substance. 
The  changes  that  take  place  in  any  substance  in  which 
the  bacteria  are  growing  are  collectively  known  as  il fer- 
mentations. "  Many  kinds  of  by-products  are  formed 
"by  the  various  forms  of  bacteria,  such  as  the  acids  pro- 
duced in  the  souring  of  milk,  and  in  the  change  of  cider 
to  vinegar,  also  in  the  "working"  of  canned  fruits  and 


Structure,  Growth  and  Distribution.  13 

vegetables.  Alkalies,  as  ammonia,  may  be  produced  as. 
in  the  fermentation  of  urine  in  the  horse  stable.  Highly 
poisonous  substances  are  sometimes  formed  in  the  bodies 
of  animals  by  the  disease-producing  bacteria. 

Distribution  of  bacteria.  Bacteria  are  more  univer- 
sally distributed  than  any  other  form  of  life.  They  be- 
come very  abundant  where  conditions  for  growth  are 
suitable,  particularly  where  a  fitting  supply  of  food  i» 
fcund.  The  soil  is  teeming  with  germ  life,  for  the  dead 
tissues  of  both  plant  and  animal  life  find  their  way  to 
the  soil.  As  most  of  this  material  is  found  in  the  upper 
part  of  the  soil,  the  bacteria  are  naturally  more  abund- 
ant here  than  in  the  subsoil.  Some  of  the  kinds  occur- 
ring in  the  soil  are  quite  indispensable  to  the  life  of 
higher  plants,  since  they  aid  in  the  preparation  of  the 
food  for  plants. 

Next  to  the  soil,  the  intestinal  canal  of  animals  sup- 
port a  large  and  varied  bacterial  flora.  The  blood,  th& 
different  internal  organs  such  as  the  liver  and  spleen, 
or  the  muscles  contain  few  or  no  bacteria,  but  in  the 
alimentary  tract  from  the  mouth  to  the  rectum,  bacteria 
are  found  in  varying  numbers. 

Water  is  also  to  be  looked  upon  as  one  of  the  natural 
habitats  of  bacteria,  for  it  always  contains  food  sub- 
stances in  greater  or  less  abundance.  As  a  rule  the 
number  of  bacteria  in  water  depends  on  the  relation  of 
the  water  to  the  soil.  Surface  streams  usually  contain 
many  bacteria,  especially  when  the  water  from  culti- 
vated fields  drains  into  the  stream.  In  shallow  wells 
that  receive  the  drainage  from  the  upper  layers  of  the 
soil,  bacteria  also  abound.  As  the  water  percolates 
through  the  soil  the  bacteria  are  filtered  out,  hence,  the 
water  from  deep  wells  contains  very  few.  The  number 


14  Agricultural  Bacteriology. 

found  in  the  waters  of  rivers,  especially  those  of  con- 
siderable size,  and  in  lakes  is  usually  small  since  there 
are  many  factors  that  tend  to  destroy  the  bacteria. 

Most  of  the  other  places  in  which  the  bacteria  are 
found  are  not  to  be  looked  upon  as  natural  habitats, 
Tjut  rather  as  secondary  sources.  The  bacteria  may  ba 
found  almost  anywhere,  because  dust  from  the  soil  finds 
its  way  into  or  onto  every  object.  The  bacteria  of  the 
air  come  from  the  soil,  being  carried  up  by  air  currents. 
The  number  in  the  air  depends  on  the  amount  of  dust 
present;  hence,  in  cities  many  are  found  in  the  air,  in 
the  open  country  far  less,  and  in  the  air  over  large  bodies 
of  water,  none  may  be  present. 

The  bacteria  found  in  all  articles  of  food  come  from 
one  of  the  natural  habitats  of  this  form  of  life.  By 
keeping  foods  as  clean  as  possible  a  great  deal  can  be 
•done  to  preserve  them. 


CHAPTER  II. 

• 
ARTIFICIAL  CULTIVATION  OF  BACTERIA. 

The  bacteria  are  so  small  that  many  thousands  of 
them  must  'be  present  in  a  mass  before  they  can  be  seen 
with  the  naked  eye.  The  necessity  of  having  masses  of 
bacteria  of  the  same  kind  for  study  in  the  laboratory 
thus  becomes  evident,  and  since  such  masses  do  not  oc- 
cur in  nature  it  becomes  necessary  to  grow  them  arti- 
ficially. 

Food  substances.  The  substances  used  in  the  labora- 
tory upon  which  the  bacteria  can  be  grown  are  of  ani- 
mal or  vegetable  origin.  These  bacterial  foods  or  * '  cul- 
ture media, ' '  as  they  are  technically  called,  may  be  pre- 
pared from  various  vegetables,  as  potatoes  or  beets. 
Broths  made  from  meat  or  beef-extract  are  constantly 
•employed,  as  are  milk,  coagulated  egg,  and  blood-serum. 
The  composition  of  these  natural  media  are  often  modi- 
fied through  the  addition  of  various  qualifying  sub- 
stances, such  as  sugar,  peptone,  and  glycerine,  in  order 
to  make  them  more  suitable  for  the  growth  of  certain 
kinds  of  bacteria. 

All  culture  media  when  prepared  from  ordinary  ma- 
terials contain  more  or  less  bacterial  life,  because  of  the 
presence  of  the  organisms  in  the  ingredients  themselves, 
and  due  to  the  inevitable  contamination  during  the  proc- 
ess of  manufacture. 

If  the  culture  media  are  to  be  kept  for  any  length  of 
time  they  must  be  freed  from  all  living  bacteria  and 


16  Agricultural  Bacteriology. 

kept  so.  For  this  purpose  the  various  media  are  placed 
in  glass  vessels,  such  as  flasks  and  tubes,  which  are 
stoppered  with  cotton-wool.  This  cotton  plug  allows: 
the  air  to  pass  freely  in  and  out  of  the  vessel,  but  re- 
moves all  dust  and  bacteria  that%the  air  may  contain. 
It  serves  to  prevent  the  bacteria  from  entering  tlje  ves- 
sel from  the  outside  as  effectively  as  though  the  vessel 
were  sealed  air  tight. 

Sterilization.  After  the  media  is  thus  protected  from 
future  contamination,  the  contained  bacteria  are  killed1 
by  heating  the  media  to  the  boiling  point  for  a  short 
time  on  each  of  three  successive  days.  The  vegetating 
cells  are  easily  killed  but  the  spores  are  not  destroyed 
by  the  first  heating.  If  the  media  is  stored  at  ordi- 
nary temperatures,  many  of  the  spores  will  germinate 
and  form  cells  before  the  second  heating.  The  remain- 
ing spores  will  usually  sprout  by  the  third  day  and  are 
then  destroyed.  A  heating  treatment  applied  as  pre- 
scribed will  usually  render  any  food  medium  "sterile,'' 
i.  e.,  absolutely  free  from  all  living  bacteria  or  their 
spores.  When  so  treated  it -will  keep  for  an  indefinite 
period  if  protected  from  drying. 

The  vegetating  cells  and  also  the  spores  may  be  killed 
at  one  heating  but  the  exposure  must  be  very  prolonged 
or  it  must  be  made  in  a  closed  chamber  in  which  steam 
is  generated.  In  this  latter  condition  the  temperature 
can  be  raised  quickly  to  a  point  considerably  higher 
than  the  boiling  point  so  that  the  spores  will  be  killed 
in  a  few  minutes.  This  same  process  is  used  in  the 
canning  of  vegetables,  such  as  corn  and  peas.  All  such 
foods  must  be  sterile  or  they  will  soon  spoil. 

The  containers  used  to  hold  the  media  are  usually  of 
glass  and  are  rendered  free  from  all  living  bacteria  by 


Artificial  Cultivation  of  Bacteria.  17 

heating  them  in  a  hot-air  oven.  This  method  can  not 
be  used  for  culture  media  since  it  would  burn  the  same. 
Determination  of  the  number  of  bacteria  in  sub- 
stances. The  extreme  minuteness  of  the  bacteria  makes 
it  impossible  to  count  them  individually.  To  determine 
the  number  present  in  any  material  it  is  necessary  to 


FIG  6. — PLATE  CULTURE. 

Each  of  the  dots  is  a  colony  that  has  been  formed 
by  the  growth  of  a  bacterial  cell  embedded  in 
the  solid  medium.  By  counting  the  colonies,  the 
number  of  bacteria  in  the  material  examined  is 
determined. 

separate  each  organism  from  all  others  by  an  appre- 
ciable distance.  The  organisms  are  then  placed  in  an 
appropriate  food  substance  in  which  they  are  held  in 
place,  growth  occurs  and  a  mass  large  enough  to  be 


18  Agricultural  Bacteriology. 

seen  by  the  naked  eye  is  soon  obtained.  If,  for  exam- 
ple, the  number  of  bacteria  in  a  sample  of  water  is  to  be 
determined,  the  conditions  mentioned  above  are  ob- 
tained in  the  following  way.  A  definite  amount  of 
water  is  intimately  mixed  with  a  small  amount  of  beef- 
broth  to  which  gelatin  has  been  added.  This  furnishes 
a  medium  which  is  solid  at  ordinary  temperatures,  but 
which  can  be  easily  melted,  and  by  cooling  changed 
back  to  a  solid  again.  If  the  gelatin  is  at  once  cooled 
after  the  water  has  been  mixed  with  it,  the  bacterial 
cells  will  be  held  in  place  in  the  now  solid  medium.  The 
gelatin  is  then  placed  under  favorable  conditions  for 
the  growth  of  the  bacteria.  The  cells  begin  to  increase 
in  number,  and  as  their  progeny  can  not  move  away,  the 
resulting  mass  of  cells  soon  becomes  large  enough  to  be 
recognized  by  the  unaided  eye.  In  liquid  media,  such 
as  beef -broth,  the  bacteria  are  not  held  in  place  and  the 
liquid  becomes  uniformly  turbid  because  of  the  distri- 
bution of  the  bacteria  in  it. 

Each  of  the  masses  of  growth,  technically  called  a 
"colony,"  is  the  progeny  of  a  single  cell.  Thus,  if  the 
colonies  are  counted,  the  result  will  be  the  number  of 
bacterial  cells  present  in  the  substance  at  the  time  the 
cultures  were  made.  In  order  to  make  the  counting  of 
the  colonies  easy  the  mixture  of  gelatin  and  water  is 
placed  in  a  shallow  glass  dish  so  as  to  form  a  thin  layer  of 
solid  gelatin  on  the  bottom  of  the  dish.  It  is  protected 
from  the  bacteria  of  the  air  by  a  glass  cover. 

It  is  essential  if  one  is  to  determine  how  many  bac- 
teria are  present  in  the  amount  of  water  used,  that  each 
of  the  colonies  on  the  culture  plate  is  the  result  of  the 
growth  of  an  organism  present  in  the  water.  This  ne- 
cessitates that  the  food  medium,  the  glass  dish  and 


Artificial  Cultivation  of  Bacteria.  19 

everything  coming  in  contact  with  the  culture  in  any 
way  is  wholly  free  from  living  bacteria,  i.  e.,  sterile. 

Many  substances  frequently  contain  so  many  bacteria 
that  it  is  impossible  to  add  a  small  enough  amount  to 
the  gelatine  directly,  and  not  have  the  cultures  so 
thickly  dotted  with  colonies  that  it  would  be  impossible 
to  count  them.'  To  overcome  this  difficulty  a  small  but 
definite  amount  of  the  substance  is  added  to  a  definite 
amount  of  sterile  water,  and  intimately  mixed.  A 
quantity  of  the  mixture  is  then  added  to  the  melted 
gelatin.  In  this  manner  it  is  possible  to  obtain  1-1000 
of  a  drop  of  water  or  milk,  a  procedure  that  will  be 
seen  to  be  necessary  when  it  is  known  how  many  qf  the 
bacteria  there  may  be  in  a  drop  of  these  liquids. 

Pure  cultures  of  bacteria.  Since  each  colony  has  re- 
sulted from  the  growth  of  a  single  cell,  it  follows  that 
all  of  the  cells  of  the  colony  are  of  the  same  kind.  If 
a  small  bit  of  the  mass  of  growth  is  transferred  from 
the  original  colony  to  a  tube  of  fresh  food,  the  resulting 
growth  is  known  as  a  "pure  culture."  If  some  other 
form  of  bacteria  should  accidentally  fall  into  the  tube 
from  the  air  when  the  tube  is  opened,  the  culture  no 
longer  contains  a  single  kind  but  a  mixture  and  is  now 
called  an  impure  or  mixed  culture. 

The  shape  and  appearance  of  the  colonies  of  the  dif- 
ferent kinds  of  bacteria  differ  as  do  their  growth  on 
various  media.  These  differences  often  aid  the  experi- 
enced bacteriologist  in  determining  the  kind  of  bacteria 
in  the  materials  examined. 

In  order  to  separate  a  pure  culture  from  a  mixture  of 
many  kinds  or  in  order -to  determine  the  kinds  of  bac- 
teria present  in  any  substance,  essentially  the  same 
method  is  used  as  described  above. 


20  Agricultural  Bacteriology. 

Use  of  the  microscope.  The  microscope  of  necessity 
is  a  tool  of  vital  importance  to  the  bacteriologist.  The 
extreme  minuteness  of  the  bacteria  require  that  an  in- 
strument magnifying  several  hundred  diameters  be 
used.  Even  then  the  bacteria  in  an  untreated  condition 
are  very  difficult  to  see  on  account  of  their  transpar- 
ency. In  order  to  make  them  more  easily  visible  a  very 
small  amount  of  the  substance  in  which  they  are  grow- 
ing is  spread  on  a  thin  piece  of  glass  and  allowed  to 
become  perfectly  dry.  The  organisms  are  then  killed 
by  heating  gently  and  are  treated  with  various  stains 
which  impart  a  bright  color,  red,  blue,  or  purple  as  the 
case  may  be,  to  the  bacteria.  Just  as  a  red  glass  is  seen 
more  easily  than  a  piece  of  perfect  plate  glass  so  the 
stained  bacteria  are  more  easily  seen  than  the  unstained 
forms,  and,  moreover  their  size,  exact  form  and  other 
characteristics  are  more  easily  determined. 

Appearance  of  the  bacteria  under  the  microscope. 

The  appearance  of  the  individual  bacterial  cell  under 
the  microscope  can  not  vary  widely  because  of  the  limi- 
tation that  the  bacteria  are  one-celled  structures.  The 
spherical  forms  always  appear  as  tiny  dots,  the  rods  as 
dashes,  and  the  spiral  forms  as  dashes  or  lines  more  or 
less  curved  in  various  ways.  The  size  varies  somewhat, 
as  do  the  arrangement  of  the  cells  with  reference  to 
each  other,  but  the  microscope  rarely  enables  one  to 
tell  the  kind  of  bacteria  present  in  a  culture.  The  ap- 
pearance of  the  growth  on  a  large  number  of  media 
must  be  noted,  as  also  the  changes  produced  in  these 
different  food  substances.  These  serve  as  aids  to  the 
appearance  under  the  microscope  in  determining  the 
kind  of  bacteria  one  has  at  hand. 


Artificial  Cultivation  of  Bacteria.  21 

Handling  of  bacteria.  The  bacteria  are  handled  in 
the  laboratory  and  are  transferred  from  one  culture 
tube  to  another  containing  fresh  food  by  means  of  small 
platinum  wires  inserted  in  glass  handles.  These  wires 
are  rendered  germ  free  by  heating  them  in  a  flame  be- 
fore they  are  used.  By  keeping  the  culture  tubes 
plugged  with  cotton,  by  careful  use  of  the  inoculating 
needle,  and  by  using  care  at  every  step,  the  bacteriolo- 
gist works  with  the  most  dangerous  disease-producing 
organisms  without  danger  to  himself. 

Use  of  experimental  animals.  In  the  study  of  the 
disease-producing  or  pathogenic  bacteria,  it  frequently 
becomes  necessary  to  use  for  inoculation  purposes  small 
animals,  such  as  guinea  pigs,  rabbits,  white  mice,  and 
rats.  Some  forms  of  bacteria  can  not  grow  on  any  of 
the  artificial  media  but  may  develop  in  the  bodies  of 
animals,  so  that  animal  inoculation  becomes  a  necessity 
in  determining  whether  any  particular  kind  of  organ- 
ism is  able  to  produce  disease  or  not. 

Incubation  of  bacteria.  Many  of  the  bacteria  have 
acquired  parasitic  properties  and  grow  naturally  only 
in  the  bodies  of  animals.  Such  is  the  case  with  the  tu- 
bercle bacillus.  If  such  types  are  to  be  artificially 
propagated,  the  cultures  must  be  kept  under  conditions 
simulating  the  animal  body.  Hence  incubators  to  main- 
tain the  cultures  at  the  same  temperature  as  the  animal 
body  are  more  or  less  essential  in  bacteriological  work. 


SECTION  II. 

RELATION  OF  BACTERIA  TO  MILK  AND  OTHER 
DAIRY  PRODUCTS. 


CHAPTER  III. 
CONTAMINATION  OF  MILK. 

A  large  part  of  the  farming  population  of  the  country 
is  actively  interested  in  the  production  of  milk.  Every 
one  is  interested  in  milk  from  the  food  standpoint. 
How  this  important  food  product  can  be  produced  un- 
der clean  and  healthful  conditions  therefore  appeals  to 
every  one,  producer  and  consumer  alike. 

Milk  a  perishable  food.  Milk  is  produced  on  the 
farm,  (1)  for  sale  in  the  tOAvns  and  cities,  (2)  for  use 
in  the  manufacture  of  butter  and  cheese.  In  order  that 
it  shall  find  a  ready  market  in  the  city  and  that  the  but- 
ter and  cheese  made  from  it  shall  be  of  the  highest 
quality,  it  is  necessary  that  the  milk  be  produced  and 
handled  under  improved  conditions.  No  other  food  is 
produced  under  circumstances  that  permit  of  the  intro- 
duction of  such  an  amount  of  dirt  and  bacteria  as  are 
found  very  frequently  in  milk.  At  every  step  it  is  nec- 
essary to  consider  the  relation  of  bacteria  to  this  food 
product.  Many  of  the  most  important  human  foods 
are  perishable.  Eggs,  meat,  many  fruits,  and  vegeta- 


Contamination  of  Milk.  23 

bles  rapidly  undergo  changes  that  render  them  unde- 
sirable, or  even  unfit  for  human  food.  Milk  is  the  most 
perishable  food  of  all.  Produced  under  ordinary  con- 
ditions and  with  no  precautions  taken  to  preserve  it 
during  the  warmer  periods  of  the  year,  it  is  unfit  for 
use  in  twenty-four  hours. 

There  are  two  reasons  for  this  rapid  deterioration : — 
(1)  gross  contamination,  (2)  its  nature  and  composi- 
tion. The  surroundings  in  which  milk  is  produced  al- 
ways make  infection  easy.  The  high  nutritive  compo- 
sition and  the  dilution  of  its  food  ingredients  make  it 
admirably  adapted  as  a  medium  for  bacterial  growth. 
Many  of  the  bacteria  produce  changes  in  the  milk  which 
injure  the  quality  of  the  butter  and  cheese.  It  thus  be- 
comes important  to  prevent  as  far  as  possible  the  intro- 
duction of  the  bacteria  and  to  check  their  development 
in  the  milk. 

Contamination  of  milk.  Tn  order  to  prevent  the  bac- 
teria from  getting  into  the  milk,  it  is  necessary  to  know 
the  sources  from  which  they  come,  and  to  become  ac- 
quainted with  practical  means  of  exclusion.  Unless  the 
sources  are  recognized  and  something  is  known  of  their 
relative  importance,  numerous  things  will  be  done  that 
are  unnecessary,  and  often  the  essential  things  left  un- 
done. 

The  subject  of  the  contamination  of  milk  is  the  most 
important  and  fundamental  one  in  dairy  bacteriology. 
At  every  step  in  the  production  of  milk  and  in  its  treat- 
ment on  the  farm  the  farmer  is  confronted  with  this 
subject.  The  returns  he  receives  from  his  milk  are 
often  decided  by  the  wisdom  with  which  he  meets  the 
problems  concerned  in  the  production  of  clean  and 
healthful  milk. 


24  Agricultural  Bacteriology. 

The  contamination  of  milk  must  be  considered  from 
two  points  of  view: — (1)  the  economic,  that  is  the  con- 
tamination with  thos'e  forms  of  bacteria  that  cause  the 
milk  to  sour,  (2)  the  hygienic,  the  contamination  with 
those  forms  of  bacteria  that  produce  disease  in  human 
beings.  Both  of  these  phases  of  milk  contamination 
are  becoming  more  important  each  year,  as  more  is 
learned  of  the  ways  in  which  diseases  are  spread  and  as 
the  rapid  growth  of  the  cities  makes  it  necessary  to 
draw  milk  from  more  distant  sources. 

Condition  of  milk  when  formed  in  the  udder.  When 
the  milk  is  secreted  in  the  udder  of  a  healthy  cow  it  is 
sterile.  The  various  internal  organs  and  the  blood  are 
practically  sterile  in  healthy  animals,  hence  any  sub- 
stance which  is  formed  from  the  blood  must  be  sterile. 

Condition  of  the  milk  when  drawn  from  the  udder. 

If  &  sample  of  milk  is  drawn  into  a  sterile  vessel  in  such 
a  way  as  to  prevent  all  external  contamination,  it  will 
be  found  to  contain  a  greater  or  less  number  of  bac- 
teria, which  must  have  come  from  the  udder  of  the  ani- 
mal. 

The  udder  is  composed  of  the  secreting  tissue  held 
in  place  by  the  fibrous  connective  tissue.  From  the  upper 
part  of  the  glandular  secreting  tissue,  small  tubes  lead 
downward,  joining  each  other  until  they  communicate 
with  a  small  cavity  known  as  the  milk  cistern,  which 
holds  about  one  half-pint.  From  this  cistern  the  milk 
flows  into  the  teat  which  is  guarded  by  muscles,  at  the 
top  and  bottom.  A  normal  contraction  of  these  muscles 
keeps  the  milk  from  leaking  out  of  the  udder. 

The  end  of  the  teat  inevitably  becomes  soiled  with 
material  containing  bacteria.  Through  the  opening  of 


Contamination  of  Milk.  ^  25 

the  teat  the  bacteria  make  their  way  up  into  the  milk 
cistern  and  to  a  less  extent  into  the  milk  ducts,  and 
e\en  to  the  secreting  tissue  proper.  Many  forms  un- 
doubtedly enter  but  only  a  few  are  able  to  grow  to  any 
extent.  They  are  harmless  guests  and  cause  the  cow  no 
trouble.  They  are  found  in  the  milk  when  it  is  drawn, 
usually  several  hundred  in  every  cubic  centimeter. 
Since  the  bacteria  enter  the  udder  through  the  teat,  one 
should  expect  to  find  the  greater  number  in  the  lower 
part  of  the  udder,  where  they  would  be  washed  out  dur- 
ing the  first  part  of  the  milking.  As  a  rule  the  first 
streams  from  each  teat  contain  a  larger  number  of  or- 
ganisms than  those  subsequently  drawn. 

This  source  of  contamination  can  not  be  wholly 
avoided.  Material  reduction  in  numbers  may  be  pro- 
duced by  excluding  the  fore-milk  i.  e.,  the  first  few 
streams  drawn  from  each  teat.  Such  milk  should  be 
drawn  into  a  separate  container,  not  milked  on  to  the 
floor.  It  may  be  used  for  feed.  It  is  always  low  in  bat- 
ter fat.  While  such  a  method  will  reduce  the  number 
of  bacteria  in  the  milk  slightly,  it  has  no  particular 
effect  upon  the  keeping  quality  of  the  milk  since  the  or- 
ganisms found  in  the  udder  grow  very  slowly  at  ordi- 
nary temperatures  and  produce  no  marked  changes  in 
the  milk. 

Some  times  the  udder  is  invaded  by  harmful  kinds  of 
bacteria  which  grow  rapidly  and  cause  an  inflammation 
of  the  gland,  which  diseased  condition  is  known  as  gar- 
get. See  p.  144. 

Contamination  from  the  animal.  Milking  is  almost 
always  carried  on  under  conditions,  that  must  be  called 
unclean  when  it  is  considered  that  human  food  is  being 
prepared.  Conditions  are  tolerated  in  the  barn  that 


26  %        Agricultural  Bacteriology. 

would  not  be  allowed  in  the  kitchen,  and  yet,  in  both  cases 
the  preparation  of  human  food  is  in  progress.  Of  neces- 
sity it  is  difficult  to  produce  milk  in  a  wholly  clean  en- 
vironment; yet  every  effort  should  be  made  to  improve 
the  barn  conditions  as  much  as  possible. 

During  the  milking,  dust,  dirt,  and  manure  particles 
are  dislodged  from  the  udder  and  flanks  of  the  animal 
by  the  motions  of  the  milker.  These  particles  inevit- 
ably fall  into  the  open  pail.  The  amount  of  dirt  and 
manure  thus  introduced  into  the  milk  depends  almost  en- 
tirely on  the  cleanliness  of  the  animal.  If  the  flanks  and 
udder  are  coated  with  manure  and  dried  mud,  a  very 
large  amount  of  dirt  will  enter  the  milk  and  nothing 
can  prevent  it. 

As  has  been  previously  mentioned  a  prominent  source 
of  bacterial  life  is  the  intestinal  canal  of  animals.  In 
the  manure  are  found  an  immense  number  of  bacteria. 
It  requires  but  a  small  amount  of  manure  to  add  many 
thousands  of  bacteria  to  every  drop  of  milk.  The  fact 
that  the  kinds  of  bacteria  derived  from  the  manure  pro- 
duce, in  the  main,  injurious  changes  in  the  milk  (bad 
odors  and  tastes)  affecting  not  only  the  milk  but  the 
butter  and  cheese  as  well,  makes  it  highly  desirable  to 
reduce  the  contamination  from  this  source  as  far  as  pos- 
sible. 

The  dust  from  the  skin  of  the  animal  contains  large 
numbers  of  bacteria.  Esten  found  in  the  dust  taken 
from  a  curry  comb  207,000,000  organisms  per  gram  (1-30 
ounce) .  The  hairs,  even  those  from  the  cleanest  cows, 
have  large  numbers  of  bacteria  on  them. 

Prevention  of  contamination  from  the  animal.  In 
order  to  prevent  the  milk  from  being  contaminated  with 
large  quantities  of  mud  and  manure,  the  animal  must  be 


Contamination  of  Milk.  27 

kept  clean.  The  cows  must  not  have  access  to  mud 
holes,  the  yards  should  be  so  arranged  that  they  can 
not  become  muddy  during  the  wet  times  of  the  year. 

The  arrangement  of  the  stalls  should  be  such  as  to- 
prevent  contact  of  the  body  of  the  animal  with  the  ma- 
nure. This  can  only  be  accomplished  by  using  a 
manure  drop,  i.  e.  a  deep  gutter.  The  animal  can  also- 
be  kept  clean  by  the  use  of  a  stall  that  requires  her  to 
stand  well  to  the  rear  and  forces  her  forward  when  ly- 
ing down.  Many  of  the  patented  stalls  seek  to  accom- 


«  FIG.  7. — THE  MODEL  STALL. 

A   stall   of   this   type   keeps   the   animals   clean   and 
aids  greatly  in  the  production  of  clean  milk. 

plish  this  in  a  variety  of  ways.  Fig.  7  represents  a  stall 
that  accomplishes  this  purpose  in  a  most  successful  way. 
The  essential  feature  of  this  stall  is  the  placing  of  a  two 
by  three  inch  piece  of  timber  across  the  floor  of  the 
stall.  This  piece  is  so  placed  that  when  the  animal 
stands  with  her  head  close  to  the  slatted  manger,  it  will 
be  just  in  front  of  her  hind  feet.  Thus  when  the  animal 


28  Agricultural  Bacteriology. 

is  standing,  her  hind  feet  will  always  be  back  of  the 
strip  and  the  manure  fall  well  to  the  rear.  The  animal 
soon  learns  that  it  is  not  at  all  comfortable  to  lie  on  the 
-strip  and  thus  crowds  to  the  front  on  lying  down  and  is 
out  of  contact  with  the  manure.  The  clean  condition 
of  the  cows  in  the  accompanying  illustration  is  to  be 
noted.  The  photographs  were  taken  in  the  early  spring 
before  the  cows  had  shed  their  winter  coats.  Less 
than  one  hour  per  day  of  one  man's  time  was  spent  in 
cleaning  the  thirty  animals  of  the  herd.  A  stall  that 
accomplishes  this  purpose,  together  with  plenty  of 
clean  bedding  is  all  that  is  needed  to  keep  the  cattle 
clean.  These  things  are  within  the  reach  of  every 
farmer.  Concrete  is  often  used  as  a  floor  and  is  very 
desirable  on  account  of  the  easier  cleaning.  It  is  de- 
sirable, especially  in  the  colder  parts  of  the  country,  to 
cover  the  concrete  of  the  stalls  with  wood. 

Other  things  may  be  done  that  will  greatly  reduce 
the  contamination  from  the  animal.  The  long  hairs 
should  be  clipped  from  the  udder  and  flanks  and  the 
tail  should  also  be  clipped.  The  short  hair  holds 
much  less  dirt  and  the  animal  can  be  cleaned  much 
easier  in  case  she  becomes  soiled.  Cleaning  with  card 
and  brush  will  also  insure  the  removal  of  much  of  the 
loose  dirt  and  hair  from  the  skin.  This  treatment 
should  be  given  some  time  before  the  milking  time,  on 
account  of  the  dust  produced.  The  udder  and  flanks 
should  be  wiped  with  a  damp  cloth  just  before  milking. 
This  serves  to  remove  much  of  the  dust  and  prevents  the 
dislodgment  of  the  finer  dust  particles  during  the  milk- 
ing process. 

Improved  milk  pails.  In  order  to  still  further  dimin- 
ish the  contamination  from  the  animal  the  use  of  a  pail 


Contamination  of  Milk,  29 

with  a  small  opening  is  desirable.  The  larger  part  of 
the  dirt  entering  the  pail  comes  from  the  flank  rather 
than  from  the  udder.  The  dirt  is  dislodged  by  the  eon- 
tact  between  the  milker  and  the  flank  of  the  animal. 
All  this  material  finds  its  way  into  the  common  large 
topped  pail.  If  the  opening  is  restricted  to  six  inches, 
the  exposed  surface  is  greatly  lessened.  A  six  inch 
opening  is  one-fourth  as  large  in  area  as  a  twelve  inch. 
The  reduction  of  contamination  will  be  in  still  greater 
proportion  as  with  the  small  topped  pail  the  opening 
is  directly  beneath  the  udder  during  the  milking.  The 
dirt  from  the  flanks  does  not  find  its  way  so  readily 
into  this  pail  as  it  does  into  the  ordinary  pail. 

Stocking  has  shown  that  under  ordinary  barn  condi- 
tions the  number  of  bacteria  found  in  milk  drawn  into 
such  a  covered  pail  was  but  five  per  cent  of  the  number 
found  when  an  ordinary  pail  was  used,  and  with  very 
dirty  cows  but  3  per  cent. 

Many  forms  of  pails  of  this  character  have  been  sug- 
gested. All  seek  to  reduce  the  size  of  the  opening  in 
one  way  or  another.  Some  of  the  most  practical  forms 
are  represented  in  Figs.  8  and  9.  In  some  of  the  pails, 
strainers  of  cloth  or  cotton  are  used,  although  brass 
wire  gauze  is  effective  and  easier  cleaned. 

The  use  of  the  milking  machine  avoids  a  large  part  of 
the  contamination  from  the  animal  since  the  milk 
is  drawn  directly  into  a  closed  tube  through  which  it 
passes  to  the  receiving  can. 

Contamination  from  utensils.  The  various  utensils 
used  in  handling  milk  always  contain  bacteria,  the 
number  depending  on  the  cleanliness  of  the  utensnX 
which  is  determined  (1)  by  the  manner  of  washing,  (2) 
the  construction  of  the  utensil,  (3)  the  condition  of  the 


30  Agricultural  Bacteriology. 

utensil.  Cheap  tin-ware  is  usually  made  with  folded 
•seams  which  are  not  flushed  with  solder.  The  milk 
penetrates  into  the  crevices  thus  formed  and  can  not 


FIG,  8. — IMPROVED  MILK  PAILS. 

The  small  opening  is  very  efficient  in  keeping  dirt 
out  of  the  milk. 


FIG.  9. — IMPROVED  MILK  PAILS. 

The  Stadtmueller  pail  and  the  Truman  pail,  two  of 
the  most  practicable  of  the  small  topped  pails. 

l>e  removed  by  washing.  As  the  utensil  becomes  older 
the  seams  become  more  and  more  open  and  a  greater 
amount  of  material  accumulates  in  them  to  find  its  way 
into  the  milk.  Old  battered  and  rusty  tin- ware  can  not 


Contamination  of  Milk.  31 

be  well  cleaned  by  washing  unless  the  facilities  for  such 
purposes  are  much  better  than  on  the  ordinary  farm. 

All  tin-ware  should  have  a  smooth  and  unbroken  sur- 
face. Even  the  roughness  due  to  the  accumulation  of 
the  white  layer  (milk  stone)  on  the  pails  and  cans  ren- 
ders them  much  more  difficult  to  wash  and  hence  in- 
creases the  contamination  from  them.  Pressed  tin- 
ware is  preferable  but  if  the  utensils  are  made  with 
seams  the  depressions  should  be  thoroughly  flushed  with 
solder. 

The  farm  cream-separator  is  a  utensil  that  needs 
especial  care.  Often  it  is  not  the  custom  to  take  the 
machine  apart  after  each  period  of  use  and  wash  it  thor- 
oughly. When  used  for  the  evening  milk  it  is  often 
only  rinsed  out  by  passing  water  through  the  bowl. 
The  slime  that  accumulates  on  the  wall  of  the  bowl  can 
not  be  removed  in  this  way,  and  between  the  periods  of 
use,  especially  during  warm  weather,  the  bacteria  grow 
rapidly  in  the  slime.  When  milk  is  passed  through  the 
separator  in  the  morning,  a  large  part  of  these  bacteria 
find  their  way  into  the  milk  and  cream  and  may  cause 
undesirable  fermentation  changes  in  them.  The  sepa- 
rator should  be  taken  apart,  well  washed  and  scalded 
after  each  period  of  use.  Much  loss  is  caused  to  the 
farmers  of  the  country  due  to  the  diminished  returns 
received  from  butter  made  from  cream  separated  in 
dirty  farm  separators.  In  fact,  it  is  well  recognized 
that  the  general  introduction  of  the  farm  separator  has 
led  to  a  deterioration  in  the  quality  of  butter. 

Contamination  from  factory  by-products.  The 
farmer  is  accustomed  to  return  to  the  farm  the  skim 
milk  or  whey  from  creamery  or  factory  in  the  milk  can. 
If  the  can  is  at  once  emptied  and  thoroughly  washed,  no 


32  Agricultural  Bacteriology. 

especial  harm  results.  In  the  whey,  especially  in  that 
from  unclean  tanks,  are  found  injurious  forms  of  bac- 
teria that  find  their  way  from  the  whey  to  the  cheese- 
vat  through  the  medium  of  the  contaminated  and  poorly 
washed  milk  can.  In  order  to  avoid  this  source  of  loss 
a  separate  set  of  cans  should  be  used  in  which  to  return 
the  by-products  to  the  farm.  At  some  cheese  factories 
and  creameries  the  by-products  are  heated  to  the  scald- 
ing point  before  being  returned  to  the  farm.  When  so 
handled  the  results  are  essentially  as  good  as  if  a  sepa- 
rate set  of  cans  were  used. 

Washing  milk  utensils.  All  milk  utensils  should  be 
washed  as  soon  as  possible  after  using,  for  if  the  milk 
is  allowed  to  dry  on  the  surface  of  such  containers  it 
is  very  difficult  to  remove.  They  should  be  rinsed  with 
cool  or  hike-warm  water,  then  thoroughly  washed  with 
a  hot  solution  of  a  washing  powder,  as  Wyandotte  or  a 
similar  preparation,  using,  preferably,  a  stiff  brush  for 
scrubbing.  The  use  of  soap  and  soap  powders  is  to  be 
avoided  for  they  are  difficult  to  remove  by  rinsing  and 
are  not  as  effective  in  the  removal  of  the  milk  and 
grease.  The  utensils  should  be  well  rinsed  in  boiling 
water,  using  a  large  quantity,  so  that  they  will  be  thor- 
oughly scalded.  If  the  scalding  is  done  with  a  small 
amount  of  hot  but  not  boiling  water,  the  bacteria  on  the 
walls  of  the  utensils  will  not  be  destroyed.  After 
scalding  they  should  be  drained  but  never  wiped.  If 
sufficient  hot  water  is  used,  the  utensil  will  be  heated 
so  that  it  will  dry  quickly  with  no  further  attention. 
The  clean  utensils  should  be  stored  in  a  place  free  from 
dust. 

Wherever  steam  is  available,  the  cleansing  can  be- 
made  much  more   effective   by  steaming,   after  rinsing 


Contamination  of  Milk.  33 

with  clean  water.  By  this  treatment  it  is  possible  to 
destroy  practically  all  bacteria.  For  this  reason  most 
city  dairy  companies  and  even  some  cheese-factories 
and  creameries  wash  the  cans  of  their  patrons.  Where 
steam  is  not  available  the  utensils  may  be  immersed  in 
boiling  water.  Some  such  treatment  is  especially 
recommended  to  the  milk  producer  supplying  milk  to 
the  city  market. 

The  milk  producer  who  uses  a  milking  machine 
avoids  one  source  of  contamination  only  to  meet  an- 
other unless  care  is  taken  in  the  handling  of  the  ma- 
chine. The  rubber  tubes  used  in  connection  with  the 
machine  are  very  difficult  to  clean.  They  should  be 
well  rinsed  after  use  and  at  once  placed  in  a  3  per  cent 
formaldehyde  solution  in  such  a  way  that  the  entire 
tube  will  be  filled  with  the  solution.  This  will  prevent 
all  growth  of  bacteria  in  the  tubes.  If  some  such  treat- 
ment is  not  given  the  tubes,  the  milk  drawn  by  the  ma- 
chine will  be  found  to  contain  more  bacteria  than  that 
drawn  by  hand.  This  is  due  to  thek  fact  that  it  is  im- 
possible to  remove  all  of  the  milk  from  the  tubes  by 
rinsing  them,  and  since  it  is  also  impossible  to  dry  the 
inside  of  the  tubes,  conditions  are  favorable  for  bac- 
terial growth  with  the  result  that,  when  the  tubes  are 
next  used,  the  bacteria  pass  into  the  milk.  The  milking 
machine  is  an  aid  in  the  production  of  clean  milk  only 
when  used  in  an  intelligent  and  careful  manner. 

Contamination  from  the  air.  In  the  barn  air  more  or 
less  dust  is  to  be  found,  coming  from  the  feed,  bedding, 
and  dried  manure.  The  dust  particles  act  as  floats  for 
the  bacteria,  and  when  the  dust  settles  into  the  milk 
pail,  the  milk  is  contaminated  with  bacteria.  The  barn 
air  should  contain  the  minimum  of  dust  at  milking 


34  Agricultural  Bacteriology. 

time.  This  condition  is  to  be  obtained  by  not  feeding 
hay  or  other  rough,  dry  fodder  shortly  before  milking, 
by  not  carrying  on  any  dust-producing  operations  as 
bedding,  sweeping,  etc.,  just  before  milking.  The  ceil- 
ings of  the  stable  should  be  tight  so  that  dust  and  dirt 
can  not  fall  from  the  floor  above  and  the  walls  and  ceil- 
ings should  be  free  from  cobwebs. 

The  stable  should  be  of  such  construction  as  to  be 
easily  kept  clean.  Abundant  light  should  be  provided, 
because  the  same  is  beneficial  to  the  cattle  and  renders 
evident  dirty  conditions.  Abundant  ventilation  means 
less  dust  in  the  barn  air  and  hence  fewer  bacteria  to 
fall  into  the  milk. 

Contamination  from  the  milker.  The  milker  is  to  be 
looked  upon  as  an  important  factor  in  milk  contamina- 
tion. His  habits  with  reference  to  personal  cleanliness 
mirron  themselves  in  the  amount  of  dirt  he  will  get 
into  the  milk  drawn  by  him.  The  hands  of  the  milker 
should  be 'clean,  for  some  milk  is  certain  to  come  in  con- 
tact with  them  on  its  way  to  the  pail.  The  suit  which 
is  worn  during  milking  should  be  kept  for  that  purpose 
alone  and  should  be  washed  at  frequent  intervals. 

The  milking  should  always  be  done  with  dry  hands 
using  the  whole  hand  and  stripping  with  the  fingers 
avoided  as  far  as  possible.  Vaseline  can  be  used  on  the 
hands  or  on  the  teats  of  the  cow  if  desired. 

Influence  of  food  on  contamination  of  milk.  It  is  be- 
lieved by  many  that  the  bacteria  in  the  feed  or  water 
consumed  by  the  cow  pass  directly  into  the  milk  by 
way  of  the  udder.  From  what  has  been  said  it  is  evi- 
dent that  such  can  not  be  the  case.  The  feed  may  in- 
fluence the  kind  of  germs  in  the  milk  by  influencing 


Contamination  of  Milk.  35 

the  kind  in  the  manure.  Unsavory  as  it  may  sound,  a 
large  part  of  the  bacteria  in  the  milk  have  their  origin 
in  the  manure,  which,  in  one  way  or  another,  is  added 
to  the  milk. 

If  spoiled  or  wet  feeds  such  as  brewery  or  distillery 
slops  are  fed,  intestinal  troubles  may  result  with  a 
change  in  the  kind  of  bacteria  found  in  the  manure. 
Only  in  this  way  can  the  feed  influence,  in  any  consid- 
erable way,  the  bacterial  content  of  the  milk.  Moldy 
and  dusty  feeds  should  not  be  used.  The  straw  used 
for  bedding  should  be  clean.  Horse  manure  should  not 
be  used  for  bedding  in  the  cow  stalls.  If  the  feed  is 
such  as  to  render  the  manure  very  thin,  it  is  much  more 
difficult  to  keep  the  animals  clean,  thus  influencing  the 
number  of  micro-organisms  found  in  the  milk.  The  in- 
fluence of  impure  water  is  due  usually  to  the  fact  that 
the  cattle  have  access  to  a  stream  or  pond.  By  wading 
about  in  the  water  their  udders  are  soiled,  and  at  milk- 
ing some  of  the  water  bacteria  get  into  the  milk. 

Absorption  of  odors.  Milk  absorbs  many  but  not  all 
odors  very  easily  and  for  this  reason  it  should  be  kept 
in  a  place  free  from  all  pronounced  odors  of  any  kind. 
The  odors  of  certain  fruits,  as  bananas,  and  the  odor 
of  strong  silage  are  quickly  absorbed  by  milk.  It  is  a 
popular  belief  that  milk  will  not  absorb  odors  when  it 
is  warmer  than  the  surrounding  air,  but  experimentally 
it  can  be  easily  demonstrated  that  the  opposite  is  true, 
the  warm  milk  absorbing  the  odors  more  rapidly  than 
the  cold.  For  this  reason  milk  should  always  be  re- 
moved from  the  stable  as  soon  as  it  is  drawn  from  the 
animal,  for  in  the  stable  there  is  quite  certain  to  be 
some  odor  arising  frc'n  the  manure,  the  animals  them- 
selves, or  the  feed.  The  danger  of  thus  tainting  the 


36  Agricultural  Bacteriology. 

milk  is  much  less  in  a  well  ventilated  stable.    Milk  should 
never  be  strained,  aerated  or  separated  in  the  stable. 

Odors  absorbed  from  the  feed.  In  certain  feeds  such 
as  turnips,  cabbage,  rape,  and  in  many  weeds  are  found 
substances  that  give  to  the  various  plants  their  charac- 
teristic taste  and  odor.  If  a  milch  cow  is  fed  on  such 
plants,  the  peculiar  flavoring  substance  will  pass 
through  the  system  and  reappear  in  the  milk,  often  giv- 
ing to  the  milk  such  a  peculiar  taste  as  to  render  it 
useless  for  direct  consumption  or  for  butter  and  cheese 
making.  Such  feeds  should  never  be  fed  except  in 
limited  quantities  immediately  after  milking  so  that 
the  volatile  odors  may  be  eliminated  from  the  body  be- 
fore the  next  milking.  Green  rye  and  strong  silage 
should  be  fed  with  care  or  the  milk  will  be  injured. 

The  milk  from  cows  receiving  medicine  in  any  form 
should  be  excluded  from  the  supply  since  many  drugs 
pass  from  the  body  tissues  to  the  milk.  Such  milk 
may  cause  illness,  especially  in  children,  and  injure 
the  quality  of  butter  and  cheese. 

The  constituent  of  milk  that  causes  it  to  absorb  odors 
so  readily  is  the  fat.  Butter  is  more  easily  injured 
by  absorption  of  "odors  than  is  milk,  as  is  not  infre- 
quently noted  when  it  is  kept  in  an  ice-box  with  fruits, 
etc.  If  the  milk  is  tainted,  the  butter  and  cheese  are 
very  certain  to  show  the  same  flavor.  This  can  be  dem- 
onstrated by  feeding  cows  on  rape  and  making  cheese 
from  the  milk.  The  ripe  cheese  will  possess  the  flavor 
of  rape  to  such  an  extent  as  to  be  worthless. 

Contamination  under  winter  and  summer  conditions. 

It  is  often  thought  that  the  milk  produced  in  summer 
is  much  cleaner  than  the  winter  milk.     This  is  less  true 


Contamination  of  Milk.  37 

than  is  usually  believed,  for  on  too  many  farms  the 
cattle  have  access  to  places  where  they  become  soiled 
with  mud.  The  number  of  bacteria  gaming  entrance 
to  the  milk  in  the  summer  may  be  as  great  as  in  winter. 
The  udder  comes  in  contact  with  the  ground  when  the 
animal  lies  down  in  the  pasture  or  in  the  yard.  The 
dust  thus  accumulated  is  not  especially  visible,  but  its 
load  of  bacteria  reaches  the  milk. 

The  milk  house.  The  room  in  which  the  milk  is  to 
bo  strained  and  cooled,  preferably,  should  not  be  in  the 
barn,  but  at  a  short  distance  from  it.  It  should  be  far 
enough  away  so  that  the  odors  of  the  barnyard  will  not 
be  present.  The  room  should  be  provided  with  a  con- 
crete floor,  with  abundant  light  and  good  ventilation. 
The  windows  and  doors  should  be  well  screened  so  that 
flies  may  not  have  access  to  milk  and  the  utensils. 
As  will  be  seen  later  flies  are  often  carriers  of  disease- 
producing  bacteria. 

Clean  milk.  The  demand  for  clean  milk  is  increas- 
ing rapidly.  It  is  desired  not  only  because  it  keeps 
longer,  tastes  better,  and  finer  butter  and  cheese  can 
be  made  from  it,  but  also  because  dirty  milk  means  sick- 
ness and  death  to  the  children,  not  so  much  to  the  chil- 
dren of  the  country,  for  these  drink  fresh  milk  only  a 
few  hours  old  before  the  bacteria  carried  into  the  milk 
in  dust,  mud  and  manure  have  had  a  chance  to  grow 
and  thus  injure  the  milk.  But  the  city  child  consumes 
milk  which  is  at  least  a  day  old  and  very  often  two  or 
three  days  old,  in  which  the  bacteria  have  developed 
to  an  enormous  extent.  Clean  milk  is  desired  for 
cleanliness  sake.  Every  one  wishes  his  food  prepared 
and  handled  in  a  clean  manner.  Manure  in  milk  is  no 
more  to  be  tolerated  than  it  is  in  bread,  and  it  is  no  more 


38  Agricultural  Bacteriology. 

necessary  that  it  be  present  in  the  former  than  in  the 
latter. 

Essentials  in  the  production  of  clean  milk.  The 
statement  is  frequently  made  that  the  production  of 
clean  milk  means  expensive  stables,  elaborate  equip- 
ment, and  much  expenditure  of  time  and  labor,  but 
such  ideas  are  far  from  correct.  The  essential  condi- 
tions are  (1)  clean  cows,  clean  because  they  are  not  al- 
lowed to  lie  in  their  own  excreta,  or  are  not  forced  to 
wade  in  muddy  yards;  (2)  clean  utensils,  well  washed 
and  sterilized;  (3)  clean  barns;  (4)  clean  men  who  take 
pleasure  in  keeping  their  stables  and  animals  clean, 
and  who  recognize  the  important  sources  of  contamina- 
tion of  milk  and  avoid  them,  while  omitting  the  non- 
essential  things  that  figure  so  largely  in  many  of  the 
directions  for  the  production  of  clean  milk. 

The  expense  of  producing  clean  milk  need  be  but 
slightly  more  than  that  involved  in  the  production 
of  the  ordinary  grade  of  milk.  The  same  animals,  the 
same  feed,  the  same  time  spent  in  feeding  and  in  caring 
for  the  cattle,  supplemented  by  a  slight  amount  of  at- 
tention directed  to  the  important  points  is  all  that  is 
needed. 

Infection  of  milk  with  disease-producing  bacteria. 
Milk  is  often  a  means  by  which  disease  is  spread.  It 
may  serve  to  convey  the  disease-producing  germs 
from  one  animal  to  another,  from  the  cow  to  man,  or 
from  one  person  to  another  in  the  case  of  some  diseases 
not  found  in  the  cow.  Of  the  diseases  common  to  man 
and  cattle,  tuberculosis  is  the  most  important.  Of  the 
diseases  found  only  in  man  but  which  are  spread  by 
means  of  milk,  typhoid  fever  and  diphtheria  are  of 
most  concern. 


Contamination  of  Milk.  39 

Tuberculosis  of  the  cow.  As  will  be  seen  in  a  subse- 
quent chapter,  the  tubercle  germs  may  be  given  off  from 
the  body  of  the  diseased  animal  in  the  "open"  stage  of 
the  disease.  They  may  come  from  the  lungs,  intes- 
tines, and  udder.  Leaving  the  body  from  any  of  these 
sources  they  may  reach  the  milk.  In  tuberculosis  of 
the  lungs  the  cow  coughs  up  material  from  these  or- 
gans and  swallows  it.  It  is  digested,  but  the  tubercle 
bacteria  it  contains  pass  off  from  the  body  in  the  ma- 
nure. When  the  disease  affects  the  intestines,  the  ma- 
nure also  contains  the  tubercle  organisms. 

The  bacteria  are  carried  into 'the  milk  with  the  ma- 
nure aird  barn-dust.  The  udder  is  often  affected  by  the 
disease.  In  this  case  the  milk  is  certain  to  contain 
large  numbers  of  the  tubercle  organisms,  although  it 
may  be  perfectly  normal  in  appearance  and  taste. 

Milk  containing  tubercle  bacilli  is  often  a  means  of 
producing  the  disease  in  man,  especially  is  this  true 
in  the  case  of  children,  who  use  larger  quantities  of 
milk  than  do  adults  and  who  seem  to  acquire  tubercu- 
losis by  way  of  the  intestinal  tract  more  easily  than 
does  the  adult.  If  milk  containing  tubercle  bacilli  is 
fed  to  calves  and  hogs,  they  are  certain  to  be  infected. 

In  order  to  be  certain  that  the  milk  does  not  contain 
any  tubercle  bacilli  it  must  have  come  from  healthy 
animals.  Many  tuberculous  cows  may  give  milk  which 
is  perfectly  healthful,  but  sooner  or  later  the  milk  of 
such  animals  is  certain  to  contain  the  organisms  of  the 
disease.  No  one  can  tell  when  this  condition  obtains, 
hence  the  only  safe  way  is  to  reject  all  diseased  animals 
from  the  dairy  herd. 

Miscellaneous  diseases  of  the  cow.  Certain  other 
diseases  may  be  acquired  by  man  from  cattle  through 


40  Agricultural  Bacteriology. 

the  milk.  Foot  and  mouth  disease,  a  common  disease 
of  cattle  in  Germany  and  France,  is  often  so  acquired. 
Lumpy  jaw  or  actinomycosis  may  affect  the  udder  and 
the  organisms  be  given  off  in  the  milk.  Inflammation 
of  the  udder  or  garget,  especially  contagious  garget,  is 
caused  by  bacteria  that  may  produce  throat  and  intesti- 
nal troubles  in  man.  The  milk  of  any  animal  which 
shows  any  fever  in  the  udder  or  whose  milk  is  any  way 
abnormal  should  be  kept  from  the  general  supply.  It 
may  not  be  harmful,  but  it  is  the  secretion  of  a  diseased 
gland  and  should  not  be  used  as  human  food.  The 
milk  of  cows  having  chronic  diarrhea,  inflammation  of 
the  bowels,  or  that  have  not  cleaned  well  after  calving 
should  be  rejected.  In  short  the  milk  of  any  animal 
that  is  sick  or  that  is  receiving  medicine  should  not  be 
used  for  human  food. 

Typhoid  fever  and  diphtheria.  Typhoid  fever  is  an 
intestinal  disease  of  human  beings.  The  bacteria  are 
taken  into  the  alimentary  tract  with  food  or  drink  that 
has  been  contaminated  in  some  way.  The  organisms 
are  given  off  from  the  body  of  the  patient  in  the  feces 
and  urine.  These  materials  find  their  way  into  the 
sewage  which  is  so  frequently  discharged  into  rivers 
and  lakes  that  .also  serve  as  sources  of  water  supply. 
When  privies  are  used  as  in  the  country,  the  typhoid 
bacteria  may  reach  the  farm  well  by  means  of  the 
water  percolating  from  the  privy  vault  through  the 
ground  into  the  well.  If  such  contaminated  waters 
are  used  to  wash  milk  utensils,  the  milk  may  be  con- 
taminated with  the  typhoid  fever  germs.  Milk  uten- 
sils are  frequently  rinsed  with  cold  water  just  previous 
to  using.  Some  of  the  bacteria  are  certain  to  enter  the 
milk  if  the  water  is  polluted. 


Contamination  of  Milk.  41 

The  contamination  of  the  milk  may  also  occur 
through  the  agency  of  a  person  acting  as  a  nurse  and 
also  handling  the  milk.  The  hands  of  the  nurse  are 
easily  soiled  with  the  discharges  of  the  patient,  partic- 
ularly the  urine  which  often  contains  many  typhoid 
bacilli,  some  of  which  may  thus  find  their  way  into  the 
milk.  The  patient  after  recovery  still  gives  off  typhoid 
bacteria  from  his  body  for  a  longer  or  shorter  period 
and  thus  may  serve  to  contaminate  the  milk.  Such 
people,  known  as  "typhoid  carriers,"  are  one  of  the 
most  important  means  of  spreading  the  disease. 

The  ordinary  house  fly  is  one  of  the  most  common 
means  of  infecting  food  with  the  typhoid  bacillus.  If 
it  has  access  to  any  infectious  material,  it  may  readily 
carry  the  bacilli  to  the  food  in  the  kitchen  or  to  the 
milk  in  the  barn  or  milk  house.  The  privy  vault 
should  be  so  arranged  that  flies  can  not  enter  it.  The 
dwelling  house  and  also  the  milk  house  should  be  pro- 
vided with  screens  at  the  doors  and  windows. 

In  order  to  prevent  the  spread  of  typhoid  fever  all 
discharges  from  the  patients  should  be  thoroughly  dis- 
infected. No  one  who  has  anything  to  do  with  a 
typhoid  patient  should  have  anything  to  do  with  the 
milk  in  any  way  directly  or  indirectly.  The  patient, 
after  recovery,  should  not  handle  dairy  products  or 
have  anything  to  do  with  milk  utensils  until  the  con- 
sent of  a  physician  is  obtained.  This  should  be  the  in- 
variable practice  on  the  farm,  in  the  cheese-factory,  the 
creamery  and  in  the  city  milk-depot,  for  experience  has 
shown  that  a  single  case  of  typhoid  has  often  been  the 
means  of  infecting  the  milk  supply,  thus  producing 
widespread  epidemics.  There  is  no  danger  of  trans- 


42  Agricultural  Bacteriology. 

mission  of  the  disease  to  stock  as  none  of  the  domestic 
animals  acquire  typhoid  fever. 

The  tubercle  germ  can  not  grow  in  milk,  when  drawn 
from  the  animal ;  the  typhoid  bacillus  on  the  other  hand 
is  able  to  grow  in  it  at  ordinary  temperatures.  Only  a 
drop  of  polluted  water  or  the  most  minute  particle  of 
matter  containing  typhoid  bacteria  is  necessary  to  seed 
the  milk.  Because  of  the  growth  of  the  bacilli,  the 
milk  may  contain  large  numbers  of  them  by  the  time 
it,  reaches  the  consumer. 

The  diphtheria  bacillus  grows  in  the  throat  and  in 
the  nasal  passages  of  the  affected  person.  The  only 
way  in  which  it  can  reach  the  milk  is  through  the  me- 
dium of  the  nurse,  whose  hands  may  have  become  con- 
taminated or  from  the  patient  after  recovery,  for  un- 
fortunately recovery  does  not  mean  that  the  diphtheria 
bacillus  has  disappeared  entirely  from  the  throat  and 
nasal  passages.  They  may  persist  there  for  months. 
The  diphtheria  bacillus  like  the  typhoid  organism  can 
grow  in  milk  at  ordinary  temperatures.  The  milk 
from  farms  on  which  diphtheria  is  present  should  not 
be  sent  to  the  city  market.  The  same  rules  relative 
to  the  patient  should  be  enforced  as  with  typhoid  fever. 

Scarlet  fever  is  also  spread  by  milk  and  the  same 
precautions  should  be  observed  as  in  the  case  of  the 
diseases  previously  mentioned. 

Intestinal  troubles  caused  by  milk.  During  the  sum- 
mer months  the  death-rate  amongst  milk-fed  children 
in  the  cities  is  very  high.  This  is  due,  in  a  large 
measure,  to  the  intestinal  troubles  that  are  occasioned 
by  improper  food.  Milk  on  account  of  its  quick  per- 
ishability is  especially  liable  to  produce  troubles  of 
this  sort.  The  death-rate  of  children  is  greatest  among 


OF    THE 


Contamination  of  Milk.  43 

the  poorer  people  who  are  either  unable  to  keep  their 
milk  supply  in  good  condition  on  account  of  the  lack  of 
ice,  or  who  do  not  appreciate  the  proper  handling  of 
this  food  product. 

These  troubles  are  not  caused  by  any  specific  kinds 
of  bacteria  but  by  many  kinds  that  get  into  the  milk 
with  the  dirt  and  manure.  As  was  previously  pointed 
out,  the  country  child  drinks  fresh  milk,  the  child  of  the 
tenement-house  district,  old  milk.  Not  the  filth,  but 
the  bacteria  associated  with  it,  are  the  cause  of  the 
trouble.  The  remedy  is  clean  milk  and  as  fresh  as 
possible  to  the  consumer's  door. 

Poisoned  milk.  Occasionally  milk  is  the  cause  of 
trouble  due  to  the  fact  that  it  contains  poisonous  com- 
pounds formed  by  bacteria  in  their  development.  Nor- 
mally the  acid-forming  bacteria  prevent  the  growth  of 
the  harmful  kinds.  In  ice  cream,  poisonous  products 
are  more  often  found  than  in  milk,  due  to  the  practice 
of  storing  cream  during  the  cooler  times  of  the  sum- 
mer in  order  to  have  a  supply  for  the  warmer  periods. 
Some  forms  of  bacteria  can  grow  in  the  milk  and  cream 
at  the  storage  temperatures  and  produce  poisonous 
products. 


CHAPTER  IV. 
PRESERVATION  OF  MILK. 

Necessity  for  preservative  measures.  It  is  impos- 
sible to  produce  milk  that  does  not  contain  bacteria. 
Some  will  be  present  no  matter  how  much  care  is  ex- 
ercised since  those  forms  from  the  interior  of  the  udder 
<jan  not  be  avoided.  Usually  many  more  are  added  to 
the  milk  during  the  various  processes  of  handling.  If 
the  milk  is  left  to  itself,  it  will  very  soon  be  unfit  for 
use.  It  thus  becomes  necessary  to  use  some  means  of 
preserving  the  milk.  This  preservation  may  be  ac- 
complished in  a  number  of  ways:  (1)  by  removing  the 
bacteria;  (2)  by  preventing  their  growth  in  the  milk; 
(3)  "by  killing  the  bacteria  in  the  milk.  Most  frequently 
a  combination  of  two  or  all  of  these  methods  is  em- 
ployed. 

Straining  of  milk.  A  process  carried  out  on  every 
farm  and  in  every  cheese-factory,  creamery,  and  milk- 
depot  is  that  of  straining  the  milk.  This  is  primarily 
done  to  remove  the  solid  particles,  such  as  hair,  straw, 
«te.,  that  have  gained  entrance  to  the  milk.  These  sub- 
stances always  have  bacteria  on  their  surfaces,  hence 
their  removal  should  reduce  the  bacterial  content  of 
the  milk.  The  number  of  bacteria  removed  in  this  way 
irj  small,  since  the  continued  use  of  the  strainer  for  all 
the  milk  of  the  herd  or  the  supply  coming  to  the  milk- 
depot  serves  to  wash  most  of  the  bacteria  from  the  solid 
particles  removed  by  the  strainer. 


Preservation  of  Milk.  45 

The  mud  and  manure  that  enters  the  milk  is  partially 
soluble.  Not  over  one-half  of  the  manure  can  be  re- 
moved by  a  cloth  strainer.  The  dissolving  of  the  dirt 
and  manure  allows  most  of  the  bacteria  to  pass  into 
the  milk.  Straining  has  practically  no  effect  on  the 
keeping  qualities  of  the  milk.  It  is  undoubtedly  a 
legitimate  process,  although  from  the  standpoint  of  the 
consumer  in  the  city  or  in  cheese-factory  and  creamery 
much  can  be  said  against  it,  since  it  serves  to  make  the 
milk  appear  better  than  it  really  is  and  thus  deceives 
the  consumer.  The  Swiss  cheese  makers  do  not  allow 
their  patrons  to  strain  the  milk  because  they  wish  to 
know  its  actual  state  of  cleanliness. 

Cloth  strainers  may  really  be  a  source  of  contamina- 
tion rather  than  an  aid  in  the  removal  of  bacteria,  un- 
less they  are  carefully  washed  and  boiled  at  least  once 
a  day,  and  placed  where  they  will  dry  quickly  and 
thoroughly.  The  odor  that  is-  sometimes  noticable  in  the 
dish-cloth  or  the  kitchen  towel  is  due  to  the  fact  that 
in  the  moist  cloth  there  is  food  enough  to  allow  bacterial 
growth  to  take  place.  In  the  same  manner  growth  oc- 
curs in  the  milk-strainer  for  it  is  almost  impossible  to 
remove  all  traces  of  the  milk  by  washing.  This  .growth 
can  be  prevented  and  all  trouble  avoided  by  boiling  the 
cloth  each  day  in  order  to  sterilize  it  and  by  hanging  it 
where  it  will  dry  quickly. 

Filtering  of  milk.  Filters  composed  of  various  ma- 
terials as  paper,  cotton,  and  sand  have  been  employed 
for  the  filtering  of  milk.  It  was  thought  that  by  the 
use  of  finer  materials  than  cloth  the  bacteria  would  be 
removed  more  efficiently.  The  use  of  these  materials 
has  not  been  very  successful.  Unless  well  cleaned 
after  each  period  of  use  they  soon  become  sources  of 


46  Agricultural  Bacteriology. 

coDtamination  rather  than  a  means  of  removing  the 
bacteria.  The  filtering  of  milk  as  a  method  of  removal 
of  bacteria  can  never  be  a  success  since  anything  that 
would  remove  the  bacteria  would  also  remove  the  fat 
globules  as  these  are  larger  than  the  bacteria. 

Clarifying  of  milk.  When  milk  is  passed  through  a 
cream  separator,  a  slimy  mass  collects  on  the  wall  of 
the  bowl.  This  material  is  very  high  in  bacteria.  It 
was  urged  for  many  years  that  the  clarifying  of  the 
milk  was  a  successful  means  of  removing  the  bacteria. 
Although  the  bacterial  content  of  the  slime  is  very 
much  higher  than  that  of  the  milk  separated,  the  re- 
daction of  the  germ  content  of  the  milk  and  cream  is 
insignificant,  because  the  amount  of  slime  removed  is 
such  a  small  part  of  the  milk  separated.  The  clarifica- 
tion has  no  effect  on  the  keeping  qualities  of  the  milk. 
The  clarification  removes  more  efficiently  than  strain- 
ing the  insoluble  dirt  in  the  milk.  Clarified  milk 
shows  no  sediment  on  standing  and  for  this  reason  the 
process  has  been  adopted  by  many  milk-companies. 
Like  straining,  it  makes  the  milk  appear  better  than  it 
really  is  and  thus  misleads  the  consumer. 

It  is  evident  f  ronb  what  has  been  said  that  but  little 
can  be  done  in  removing  the  bacteria  from  milk  when 
once  they  have  gained  access.  The  more  successful 
way  to  preserve  the  milk  is  to  prevent  the  growth  of 
the  bacteria.  This  can  be  done  in  a  number  of  ways: 
(1)  by  the  use  of  low  temperatures,  (2)  by  the  use  of 
certain  chemicals,  which  have  an  antiseptic  action,  i.  e. 
prevent  or  retard  the  growth. 

Cooling  of  milk.  The  use  of  low  temperatures  is  the 
tlie  most  widely  used  and  the  most  efficient  means  of 


Preservation  of  Milk.  47 

preserving  milk.  As  was  previously  stated,  most  forms 
of  bacteria  grow  best  at  70°-90°  F.  If  milk  is  drawn 
and  no  effort  made  to  cool  it,  the  temperature  is  such 
^s  to  favor  bacterial  growth  except  during  the  coldest 
periods  of  the  year  and  the  milk  spoils  quickly.  If  the 
milk  is  cooled  to  50°  F.  by  the  use  of  cold  water,  or 
water  and  ice,  and  maintained  at  this  temperature,  it 
will  keep  several  times  as  long  as  if  uncooled,  for  the 
reason  that  many  forms  of  bacteria  do  not  grow  at 
50°  F.  and  all  kinds  grow  slowly. 

The  cooling  should  be  done  immediately  after  the 
milk  is  drawn.  It  should  be  done  not  only  in  the  sum- 
mer but  also  in  the  winter.  More  trouble  is  often  had 
with  the  milk  supply  in  the  winter  than  in  the  summer, 
largely  because  the  farmers  do  not  recognize  the  neces- 
sity of  cooling  the  milk  during  the  colder  season.  A 
ten  gallon  can  of  milk,  warm  from  the  cow,  requires 
hours  to  reach  50°  when  placed  in  a  room  having  a 
temperature  of  40°-^45°  F.  This  temperature  is  re- 
required  by  the  city  of  New  York,  and  the  milk  must 
not  be  above  50°  when  it  reaches  the  city.  Such  regu- 
lations are  necessary  when  the  milk  must  be  shipped 
hundreds  of  miles  as  is  the  case  with  the  larger  cities. 
The  milk  received  by  the  consumer  in  the  large  city  is 
often  of  better  quality  than  that  sold  in  the  smaller 
places,  because  more  attention  is  paid  to  cooling  the 
milk  and  to  keeping  it  cold. 

Milk  intended  for  the  creamery  and  cheese'  factory 
should  be  cooled.  This  is  especially  true  of  the  even- 
ing milk.  If  the  morning  milk  is  to  be  delivered  at 
once  to  the  cheese  factory,  it  need  not  be  cooled.  The 
bad  effects  of  mixing  night  and  morning  milk  is  due  to 
the  raising  of  the  temperature  of  the  night  milk  by  the 


48  Agricultural  Bacteriology. 

addition  of  the  warm  milk.  If  the  morning  milk  is- 
well  cooled  before  mixing,  no  bad  effects  will  be  noted. 
The  milk  is  best  cooled  by  the  use  of  an  apparatus 
such  as  the  Champion  or  Star  coolers.  These  cool  the 
milk  by  causing  it  to  run  in  a  thin  stream  over  a  metal 
surface,  on  the  opposite  side  of  which  is  the  cooling 
agent.  The  milk  may  be  cooled  in  tall  narrow  cans  by 
placing  them  in  cold  water,  in  this  case  the  milk  should 
be  stirred  at  intervals  otherwise  the  cooling  goes  on 
very  slowly.  The  best  plan  is  to  cool  to  55°-60°  F.  by 
the  use  of  a  cooler,  then  to  set  the  cans  in  a  vat  of  ice 
water.  The  cooling  of  milk  should  be  done  in  a  pure 
air.  free  from  dust  and  all  odors,  otherwise  the  milk  is 
likely  to  be  injured. 

Aeration  of  milk.  In  the  past  many  claims  have  been 
made  concerning  the  benefits  to  be  derived  from  the 
aeration  of  milk.  It  is  certain  that  nearly  all  the  good 
effects  ascribed  to  aeration  are  due  to  the  cooling 
which  all  processes  of  aeration  produce.  If  the  aera- 
tion should  be  carried  out  with  warm  air,  no  beneficial 
effect  would  be  noted.  The  gases  given  off  from  the 
milk  during  the  aeration  may  make  the  can  of  milk 
show  a  less  objectionable  odor  when  opened  at  the  fac- 
tory or  milk-depot,  but  it  is  certain  that  the  quality  of 
the  milk  is  not  improved  from  the  standpoint  of  the 
consumer  and  that  better  cheese  can  not  be  made  from 
the  aerated  milk. 

Use  of  antiseptics  in  milk.  The  chemicals  most  often 
used  to  preserve  milk  are  bicarbonate  of  soda  (baking 
soda),  borax,  boracic  acid,  salicylic  acid,  and  formalin. 
All  of  the  commercial  preservatives  contain  one  of 
these  chemicals,  usually  formalin,  since  this  is  the 


Preservation  of  Milk.  49 

cheapest  and  most  efficient.  The  use  of  preservatives 
is  prohibited  by  law  in  every  state  and  their  use,  if  de- 
tected, punishable  by  fine.  Their  use  is  prohibited 
since  these  substances  are  looked  upon  as  injurious  to 
human  health.  There  is  not  much  temptation  for  the 
farmer  to  use  them,  the  city  dealer  is  more  tempted, 
since  by  their  use  he  can  carry  over  to  the  next  day  the 
surplus  milk  and  economize  in  the  use  of  ice.  One 
ounce  of  formalin  costing  two  cents  added  to  1,000 
pounds  of  milk  will  cause  it  to  keep  for  twenty-four  to 
forty-eight  hours  longer  than  it  otherwise  would. 

Bicarbonate  of  soda  does  not  prevent  the  growth  of 
bacteria,  but  does,  by  neutralizing  the  acid  formed,  de- 
lay the  time  when  the  milk  begins  to  taste  sour.  The 
remainder  of  the  substances  mentioned  act  by  retard- 
ing the  growth  of  the  bacteria. 

Pasteurization  of  milk.  As  has  been  stated,  the  bac- 
teria, especially  the  vegetative  forms,  are  easily  killed 
by  heat.  The  temporary  preservation  of  food  by  heat- 
ing is  a  common  custom.  It  is  constantly  made  use  of 
by  the  housewife  in  order  to  save  some  food  that  she 
knows  will  be  spoiled  in  a  short  time  if  it  is  not  so- 
treated. 

When  this  process  is  applied  to  milk  in  the  house- 
hold or  on  a  commercial  scale  it  is  known  as  pasteuriza- 
tion. It  received  its  name  from  the  originator  of  the 
method,  Pasteur,  the  great  French  bacteriologist,  who 
first  used  it  for  the  preservation  of  the  wines  of  his 
native  district  in  France.  It  was  later  used  by  brew- 
ers in  order  to  prevent  the  formation  of  sediment  in 
beers.  Today  much  of  the  bottled  beer  is  pasteurized. 
The  process  was  later  adopted  by  the  dairy  industry, 
and  here  has  been  widely  used.  The  process  is  carried 


50  Agricultural  Bacteriology. 

out  for  two  reasons:  (1)  to  prolong  the  time  during 
which  the  milk  will  be  fit  for  use  in  the  household,  (2) 
to  destroy  any  pathogenic  bacteria  the  milk  may  hap- 
pen to  contain. 

In  Germany  milk  is  usually  heated  in  the  home.  Hot 
milk  is  a  regular  item  on  the  bill  of  fare  of  all  German 
restaurants.  The  milk  used  for  tea  and  coffee  is  also 
heated.  This  same  custom  also  prevails  in  many  of  the 
southern  countries  as  Mexico  and  Cuba.  The  people 
of  these  countries  are  accustomed  to  the  peculiar  taste 
of  heated  milk,  which  is  objectionable  to  the  American, 
accustomed  to  raw  milk.  In  commercial  pasteurization 
it  is  necessary  to  produce  an  article  that  the  consumer 
will  like.  Therefore  the  demand  here  is  for  a  milk  that 
shows  no  abnormal  flavor  such  as  a  cooked  taste. 
Heated  milk  not  only  acquires  this  taste,  but  it  loses 
its  power  of  creaming  to  a  great  extent.  Its  property 
of  curdling  with  rennet  is  also  injured.  If  cream  is 
pasteurized,  it  appears  thinner  than  raw  cream.  All 
of  these  are  objectionable  changes  from  the  standpoint 
of  the  consumer. 

As  commercial  pasteurization  is  done  largely  to  pre- 
serve the  milk,  the  temperature  must  be  sufficient  to 
kill  most  of  the  bacteria  present,  and  especially  the  dis- 
ease-producing types.  The  most  resistent  of  these  is  the 
tubercle  bacillus  and  this  of  all  the  pathogenic  bacteria 
is  most  often  to  be  found  in  milk.  It  has  been  deter- 
mined by  careful  trials  that  if  the  milk  is  heated  to 
140°  F.  for  twenty  minutes,  the  tubercle  bacilli  will  be 
destroyed,  or  if  raised  to  160°  F.  and  the  exposure 
made  for  a  moment  they  will  also  be  killed.  Both  of 
these  ways  are  used  in  commercial  work.  The  first  is 
done  in  the  discontinuous  pasteurizing  machines  in 
which  the  milk  is  heated  for  any  length  of  time  to  any 


Preservation  of  Milk.  51 

desired  temperature.  Where  large  quantities  of  milk 
are  to  be  treated,  the  "continuous  flow"  machines  are 
used,  through  which  the  milk  passes  in  a  constant 
stream. 

Household  pasteurization  of  milk.  It  is  often  desir- 
able to  pasteurize  the  milk  to  be  used  in  the  home, 
especially  that  intended  for  children,  and  when  the 
milk  comes  from  cows  not  known  to  be  free  from  tuber*- 


FIG.  10. — A  HOME-MADE  PASTEURIZER. 
The  tumbler  prevents  the  formation  of  a  membrane 
on    the    milk    during   the   heating    and    also    pro- 
tects the  mouth  of  the  bottle  from  dust. 

culosis.  The  process  can  be  easily  carried  out  in  milk 
bottles  or  fruit  jars.  These  should  be  closed  in  some 
way  in  order  to  prevent  the  formation  of  the  "skin" 
that  forms  on  milk  heated  in  an  open  vessel.  This 
membrane  has  a  protective  influence  on  the  bacteria 
embedded  in  it.  The  bottles  are  placed  in  a  vessel  hav- 
ing a  false  bottom  to  avoid  breaking  them.  The  vessel 
is  filled  with  water  to  the  height  of  the  milk  in  the 


52  Agricultural  Bacteriology. 

bottles.  The  water  is  heated  to  150°  F.  and  kept  at 
this  temperature  for  twenty  minutes.  The  bottles  of 
milk  are  then  removed  and  cooled  at  once. 

In  the  pasteurizing  process  the  bacteria  that  do  not 
form  spores  are  killed,  but  the  spores  are  not  destroyed. 
If  the  heated  milk  is  not  cooled  rapidly  and  kept  cold, 
these  spores  will  germinate  and  by  their  rapid  growth 
the  milk  will  soon  be  rendered  unfit  for  use.  Only 
small  quantities  of  milk  should  be  treated  at  one  time, 
no  more  than  can  be  used  in  twenty-four  hours.  The 
change  which  pasteurized  milk  undergoes  will  be  dis- 
cussed under  milk  fermentations,  p.  58. 

In  efficient  pasteurization  at  least  99  per  cent  of  the 
bacteria  should  be  killed.  The  better  the  quality  of  the 
raw  milk,  the  better  will  be  the  pasteurized  milk.  It 
is  not  a  process  by  which  poor  milk  that  has  abnormal 
odors  or  tastes  can  be  made  unobjectionable. 

Condensed  milk.  Condensed  milk  is  prepared  by 
adding  to  the  milk  a  quantity  of  cane  sugar  and  evapo- 
rating a  part  of  the  water  in  a  vacuum  until  the  milk 
has  the  consistency  of  a  thick  syrup.  This  milk  will 
keep  for  the  reason  that  its  concentration  is  so  great 
that  the  bacteria  tha<t  it  contains  are  unable  to  grow. 
If  it  is  diluted  with  water,  they  begin  to  grow  and  the 
milk  soon  spoils.  Unsweetened  condensed  milk  is  also 
made.  This  has  the  consistency  of  thick  cream  and 
keeps  because  the  cans  of  milk  have  been  sterilized  in 
steam  sterilizers  in  exactly  the  same  manner  as  canned 
corn  and  peas  are  treated. 

Milk  is  also  preserved  by  drying  it  until  a  powder  is 
obtained.  The  drying  is  done  in  a  number  of  ways  all 
of  which  have  been  patented  by  the  inventors.  The 
milk  powder  is  used  largely  by  bakers. 


CHAPTER  V. 
FERMENTATIONS  OF  MILK. 

A  large  number  of  kinds  of  bacteria  enter  the  milk 
during  its  production  on  the  farm.  From  the  udder, 
the  exterior  of  the  animal,  the  manure,  the  barn-dust, 
utensils,  and  milker  come  many  kinds  of  bacteria, 
yoasts,  and  molds.  Many  of  these  micro-organisms  can 
grow  in  milk. 

Composition  of  milk.  Milk  is  composed  of  about  87 
p*.T  cent  water,  in  which  is  dissolved  about  5  per  cent 
of  milk  sugar  (lactose),  various  salts,  as  common  salt, 
calcium  phosphate,  etc,  and  0.5  per  cent  of  albumen,  a 
substance  resembling  the  white  of  egg.  In  suspension 
in  the  milk  there  is  2-4  per  cent  of  casein,  the  substance 
that,  gives  to  skim  milk  its  whitish  color  and  makes  up 
the  larger  part  of  the  curd  in  sour  milk. 

Milk  is  a  perfect  food  for  animals  and  also  for  most 
bacteria.  The  different  kinds  when  growing  in  milk 
use  the  various  substances  it  contains  as  food.  From 
these  they  produce  many  products  which  alter  the  milk 
as  to  appearance,  odor,  and  taste.  The  various  changes 
produced  are  known  as  the  fermentations  of  milk,  and 
are  designated  by  the  name  of  the  most  important  by- 
product formed.  Thus,  the  souring  of  milk  is  called 
the  lactic  acid  fermentation,  because  lactic  acid  is  the 
most  prominent  substance  in  this  change. 

Souring  of  milk.  The  souring  or  acid  fermentation 
of  milk  is  so  common  a  change  that  it  is  looked  upon  as 


54  Agricultural  Bacteriology. 

a  perfectly  normal  occurrence.  Indeed  any  milk  that 
does  not  sour  when  kept  at  ordinary  temperatures  for 
some  time  is  regarded  with  suspicion  and  is  thought  to 
have  been  treated  with  preservatives.  The  souring  of 
aiilk  is  not  an  inherent  property,  but  is  due  to  certain 
kinds  of  bacteria  that  gain  entrance  to  it  after  its  with- 
drawal from  the  cow.  These  bacteria  are  found  uni- 
versally distributed  and  unless  precautions  are  taken 
to  exclude  them,  they  are  certain  to  enter  the  milk. 

The  bacteria  causing  the  souring  of  milk  use  a  part 
of  the  milk  sugar  as  food,  forming  from  it  lactic  acid. 
This  substance  is  not  a  solid  like  the  sugar  but  a  syrup- 
like  liquid,  having  no  color  or  odor  and  a  sour  taste. 
The  bacteria  producing  the  change  are  known  as  the 
lactic  acid  bacteria.  The  acid  they  form  gives  the  fer- 
mented milk  its.  sour  taste  and  causes  it  to  curdle. 
Milk  that  contains  about  0.3  per  cent  of  acid  tastes 
sour  and  curdles  when  heated.  As  the  bacteria  con- 
tinue to  develop  the  acidity  increases.  At  0.6  per  cent 
the  milk  curdles  at  ordinary  temperatures.  When  the 
acidity  reaches  about  1  per  cent,  bacterial  growth 
ceases  and  no  more  acid  is  formed.  The  bacteria  like 
all  other  forms  of  life  are  injured  by  their  own  by-pro- 
ducts unless  these  are  removed.  In  milk  the  acid  is 
formed  in  such  quantities  as  to  cause  ultimately  the 
death  of  the  cells.  The  bacteria  in  the  milk  can  not  get 
away  from  the  acid  they  have  produced,  hence  growth 
ceases,  although  plenty  of  food  remains.  If  all  of  the 
sugar  of  the  milk  were  changed  to  acid,  the  acidity  would 
be  4  per  cent,  instead  of  1  per  cent. 

Kinds  of  lactic  acid  bacteria.  The  lactic  acid  bac- 
teria come  from  various  sources.  One  type  is  often 
found  in  the  dust  coming  from  the  skin  of  the  animal 


Fermentations  of  Milk.  55 

and  in  the  dust  of  the  barn.  They  are  also  found  on  the 
milk  utensils.  Another  type  is  found  in  great  numbers 
in  the  manure.  The  first  is  a  desirable  form  and  is  nec- 
essary in  the  making  of  butter  and  cheese,  the  latter  is 
very  undesirable  in  every  way. 

The  number  of  lactic  acid  bacteria  in  freshly  drawn 
milk  is  always  very  small,  often  aggregating  not  more 
than  one  in  one  thousand  of  the  total  number  of  bacteria 
present.  In  sour  milk,  99  per  cent,  of  the  bacteria  are 
lactic  organisms.  This  great  change  in  the  flora  is  due 
to  the  fact  that  the  lactic  bacteria  find  more  favorable 
conditions  for  growth  in  milk  at  ordinary  temperatures 
than  any  other  kind  that  enters  the  milk.  They  grow 
rapidly  and  the  acid  they  produce  is  antagonistic  to 
many  other  species.  Meat,  eggs,  and  animal  foods  in 
general  putrefy.  Milk  does  not  under  ordinary  condi- 
tions, because  the  acid  formed  by  the  lactic  bacteria  pre- 
vents the  growth  of  the  putrefactive  forms,  just  as  vine- 
gar keeps  pickles  from  rotting.  Meat  can  be  preserved 
by  placing  it  in  milk  in  a  stoppered  bottle.  If  it  were 
not  for  the  lactic  bacteria,  milk  instead  of  having  a 
pleasant  taste  and  an  agreeable  smell,  would  putrefy  and 
give  off  as  offensive  odors  as  do  meat  and  eggs.  This  is 
shown  when  a  little  milk  is  spilled  onto  the  stable  floor 
or  into  the  water  of  a  cooling  vat.  The  lactic  bacteria 
are  to  be  looked  upon  as  the  friends  of  man.  They  are 
perfectly  harmless  and  even  beneficial  to  him.  Butter- 
milk, a  form  of  sour  milk,  is  enjoyed  by  most  people  as 
a  refreshing  drink.  It  contains  millions  of  lactic  acid 
bacteria  in  every  drop.  Clabber,  curds,  and  cottage- 
cheese  are  other  forms  of  sour  milk  and  are  widely  used 
as  human  food. 

The  curd  which  the  desirable  type  of  acid-forming  bac- 


56  Agricultural  Bacteriology. 

teria  produce  in  milk  is  perfectly  homogeneous,  showing 
no  holes  due  to  gas  or  no  whey  expressed  from  the  curd. 
The  odor  is  agreeable,  the  taste  sour,  but  not  bitter  or  of- 
fensive in  any  way. 

The  lactic  bacteria  do  not  form  spores  and  hence  are 
easily  killed,  if  milk  is  heated.  If  milk  is  pasteurized 
and  subsequently  kept  free  from  lactic  bacteria,  it  will 
not  sour,  but  will  putrefy  due  to  the  development  of  the 
spores  not  killed  by  the  heating.  Often  the  first  sign  of 
spoiling  in  pasteurized  milk  is  the  appearance  of  a  bitter 
or  other  undesirable  taste.  Frequently  it  does  not  cur- 
dle for  a  long  time.  One  of  the  dangers  in  the  use  of 
pasteurized  milk  is  the  fact  that  the  consumer  has  no  way 
of  telling  how  old  it  is.  It  may  appear  normal  in  every 
way  and  yet  be  harmful  to  the  health. 

The  lactic  bacteria  grow  best  at  temperatures  from 
70°-95°  F.  If  the  milk  is  cooled  below  50°,  growth  goes 
on  very  slowly,  at  still  lower  temperatures,  32°-35°,  the 
growth  of  lactic  bacteria  is  wholly  prevented,  but  other 
types  develop  which  may  cause  the  milk  to  become  harm- 
ful. 

It  is  a  widespread  belief  that  thunder  storms  cause  the 
milk  to  sour.  Electricity  has  no  effect  on  milk,  the  ap- 
parent effect  is  due  to  the  high  temperatures  that  always 
accompany  such  storms,  causing  the  bacteria  to  grow 
more  rapidly. 

Undesirable  lactic  bacteria.  The  desirable  types  of 
lactic  bacteria  produce  other  by-products  than  the  lactic 
acid  and  to  these  is  due  the  odor  of  sour  milk.  The  un- 
desirable lactic  germs  form  some  lactic  acid  but  larger 
amounts  of  other  acids  such  as  acetic  acid.  They  also 
form  gaseous  by-products  that  give  to  the  milk  an  ob- 
jectionable odor  and  taste,  injuring  it  especially  for  but- 


Fermentations  of  Milk.  57 

ter  and  cheese  making.  These  forms  come  from  dirt  and 
manure.  They  are  present  in  milk  in  greater  or  less 
numbers,  depending  upon  the  degree  of  cleanliness  used 
in  producing  and  handling  milk.  If  they  are  numerous 
in  a  sample  of  milk,  the  curd  will  be  filled  with  gas-holes, 
instead  of  having  the  homogeneous  appearance  of  the 
curd  from  good  milk.  The  curd  may  even  be  so  filled 
with  gas  as  to  float  on  the  surface  of  the  whey.  If  these 
forms  are  few  in  number  and  the  desirable  ones  predomi- 
nate, the  gas  holes  will  be  less  abundant.  These  bacteria 
form  no  spores,  and  hence  are  not  found  in  pasteurized 
milk.  They  grow  at  somewhat  higher  temperatures 
(95°-105°  F.)  than  the  desirable  lactic  bacteria. 

Abnormal  fermentations  of  milk.  The  acid  fermen- 
tation of  milk  by  reason  of  its  common  occurrence  is 
looked  upon  as  a  normal  change.  Various  other  types  of 
fermentations  that  are  quite  different  from  the  acid  fer- 
mentation and  hence  are  called  abnormal  fermentations 
or  milk  faults,  appear  now  and  then  in  milk. 

Sweet  curdling  of  milk.  Milk  may  curdle  and  yet 
the  taste  be  perfectly  sweet.  It  is  evident  that  the  curd- 
ling in  this  case  must  be  due  to  some  other  factor  than 
the  lactic  acid.  As  is  well  known  sweet  milk  may  be 
curdled  by  the  use  of  rennet  which  is  prepared  from  the 
fourth  stomach  of  the  young  calf.  The  rennet  used  in 
cheese  making  comes  from  this  source.  Rennet  will 
curdle  several  times  its  weight  of  milk  in  a  short  time. 
Substances  such  as  rennet  are  called  enzymes.  All  the 
digestion  in  the  alimentary  tracts  of  man  and  animals  is 
carried  on  by  enzymes  in  the  saliva,  the  gastric  juice,  the 
pancreatic  juice,  and  the  intestinal  fluids. 

Many  bacteria  form  enzymes  of  various  kinds.     The 


58  Agricultural  Bacteriology. 

putrefactive  ones  produce  an  enzyme  similar  to  rennet. 
When  these  forms  are  numerous,  i.  e.,  more  abundant 
than  the  sour  milk  bacteria,  the  milk  may  curdle,  al- 
though remaining  quite  sweet.  If  the  milk  is  kept  for 
some  time  after  curdling,  it  will  be  noted  that  the  curd 
becomes  soft  and  reduced  in  amount  due  to  its  digestion 
by  other  enzymes  that  resemble  trypsin  found  in  the  pan- 
creatic juice  of  animals. 

Many  of  the  putrefactive  bacteria  form  spores.  These 
spores  are  not  destroyed  in  the  pasteurization  of  milk. 
Due  to  the  development  of  these  spores,  the  pasteurized 
milk  often  curdles  although  it  still  tastes  sweet.  The- 
curd  is  soft  and  large  amounts  of  whey  separate  from  it. 
Such  milk  is  not  wholesome,  even  before  it  shows  any 
signs  of  curdling,  and  it  may  be  dangerous  to  human  be- 
ings, especially  to  children.  The  organisms  producing 
these  changes  get  into  milk  from  manure  and  dirt.  They 
are  especially  numerous  in  dust  from  hay,  straw,  and 
corn  fodder.  Such  feeds  should  not  be  fed  until  after 
milking.  These  bacteria  do  not  find  such  favorable  con- 
ditions for  growth  in  milk  as  do  the  lactic  organisms. 
The  latter  by  the  acid  they  produce  render  the  milk  still 
less  favorable  for  the  putrefactive  germs. 

Slimy  fermentation  of  milk.  One  of  the  most  fre- 
quent abnormal  fermentations  is  the  slimy  or  ropy 
change.  Such  a  condition  may  appear  when  the  milk  is 
drawn  from  the  cow,  in  which  case  it  is  usually  due  to  in- 
flammation of  one  or  more  quarters  of  the  udder.  When 
the  trouble  is  due  to  bacteria,  the  milk  becomes  slimy  a 
day  or  so  after  it  is  withdrawn  from  the  animal.  The 
causal  organisms  produce  a  slimy  substance  in  milk, 
sometimes  in  such  abundance  that  the  milk  can  be  drawn 
out  into  long  threads. 


Fermentations  of  Milk. 


59 


The  greatest  amount  of  trouble  with  slimy  milk  occurs 
during  the  warmest  weather  and  in  bottled  milk  that  has 
been  kept  in  a  refrigerator.  The  cream  is  often  slimy, 
while  the  lower  layers  are  apparently  normal.  In  other 
cases  the  entire  mass  of  milk  be- 
comes thick  and  viscous.  The  bac- 
teria producing  the  first  type  are 
aerobic  and  grow  best  at  low  tem- 
peratures. Outbreaks  of  this  trou- 
ble do  not  usually  persist  for  any 
length  of  time,  if  care  is  taken  to 
sterilize  thoroughly  the  milk  uten- 
sils. The  bacteria  causing  the  trou- 
ble do  not  form  acid. 

The  second  type  in  which  the  en- 
tire mass  of  milk  becomes  slimy  is 
usually  due  to  bacteria  that  form 
acid.     The  milk  is  curdled,  but  the 
curd  instead  of  b^ ing  easily  broken 
up  as  in  the  normal  acid  fermenta- 
tion is  very  ropy.     This  type  of  fer- 
mentation is  rare.    Tn  Norway  slimy 
milk  is  prepared  for  human  food. 
It  has  an  agreeable  acid  taste  much 
like  the  taste  of  butter-milk.     It  is 
very  ropy  and  appears  unappetiz- 
FIG.  11.— SLIMY  MILK.  ing  to  one  not  accustomed  to  it.     In 
Holland  ropy  whey,  which  is  pro- 
duced by  much  the  same  kind  of  bacteria  as  the  Norwe- 
gian "ropy  milk,  is  used  in  the  making  of  Edam  cheese  in 
order  to  overcome  trouble  in  handling  poor  milk,  just 
as  the  American  cheese  maker  uses  lactic  acid  bacteria 


60  Agricultural  Bacteriology. 

contained  in  sour  milk  as  &  starter  to  prevent  gassy 
cheese. 

None  of  the  ropy  fermentations  are  harmful  as  far  as 
health  is  concerned,  but  they  are  often  the  cause  of  con- 
siderable loss  to  the  milk  dealer.  They  do  not  appear  to 
injure  the  use  of  milk  for  butter.  The  source  of  the  bac- 
teria in  some  of  the  outbreaks  studied  has  been  found  to 
be  the  water  to  which  the  cows  had  access. 

Alcoholic  fermentation  of  milk.  As  is  well  known  in 
order  to  produce  any  of  the  fermented  drinks,  such  as 
beer  or  whiskey,  the  wort  or  mash  (the  infusion  of  barley 
or  other  grain  used)  is  seeded  with  yeasts,  which  act  on 
the  sugar  formed  from  the  starch  of  the  grain,  producing 
alcohol  and  carbon  dioxide.  None  of  the  bacteria  pro- 
duce alcohol  in  appreciable  amounts,  this  property  being 
confined  in  the  main  to  the  yeasts.  The  ordinary  type 
of  yeasts  can  not  ferment  milk  sugar,  but  in  milk,  butter, 
and  cheese,  yeasts  are  found  that  possess  this  property. 
"When  these  are  numerous  in  the  milk  they  may  injure 
the  butter  and  cheese,  giving  these  products  a  yeasty 
flavor  and  odor.  Through  the  gas  produced  from  the 
sugar,  holes  may  be  formed  in  the  cheese  and  not  infre- 
quently gas  is  formed  in  such  abundance  as  to  cause  the 
cheese  to  crack  open. 

Yeasts  grow  best  in  an  acid  medium.  This  is  shown 
by  the  ease  with  which  all  fruit  juices,  as  apple  and  grape 
juice,  undergo  alcoholic  fermentation,  even  when  no  yeast 
is  intentionally  added.  Wild  yeasts  occur  in  sufficient 
numbers  on  the  surface  of  the  fruit  to  seed  the  juice.  In 
less  acid  substances  the  bacteria  appear  first.  In  %hey 
vats  that  are  not  carefully  cleaned,  a  favorable  place 
exists  for  yeast  growth.  The  whey  becomes  acid  due  to 
the  growth  of  the  acid-forming  bacteria,  and  as  it  still 


Fermentations  of  Milk.  61 

contains  sugar,  consequently,  conditions  are  favorable 
for  yeast  development.  Milk  cans  in  which  sour  whey 
is  carried,  unless  carefully  washed,  may  serve  to  contam- 
inate the  milk  to  such  an  extent  as  to  produce  trouble  in 
cheese  factories. 

The  use  of  alcoholic  drinks  seems  to  have  been  more  or 
less  common  with  nearly  every  type  of  people.  The 
Egyptians  made  beer  from  the  grain  they  raised.  The 
nomadic  tribes,  having  no  grain,  discovered  methods  of- 
making  alcoholic  drinks  from  the  milk  furnished  by  their 
herds  of  cattle,  goats,  and  horses.  In  Russia  such  a  fer- 
mented drink,  called  koumiss,  is  made  from  mare's  milk. 
In  other  countries  similar  drinks,  but  prepared  princi- 
pally from  cow's  milk,  are  called  kefir,  matzoon,  and 
leben.  They  all  have  an  acid  taste  due  to  the  acid  formed 
by  the  lactic  bacteria,  and  they  contain  nearly  half  as 
much  alcohol  as  a  light  beer.  Such  fermented  milks- 
seem  to  be  more  easily  digested  than  raw  milk,  due  un- 
doubtedly to  the  fact  that  the  casein  is  precipitated  in  a 
finely  divided  condition  and  to  the  acid  present. 

Bitter  milk.  Bitterness  in  milk  may  be  due  to  bao 
teria  or  to  certain  feeds.  Ragweed  is  often  claimed  to 
be  the  cause  of  such  milk.  If  the  feed  is  at  fault,  the 
milk  will  show  the  bitterness  when  it  is  drawn  from  the 
cow,  and  instead  of  increasing  in  intensity,  as  is  likely  to 
be  the  case  if  the  cause  is  bacterial,  the  taste  usually  be- 
comes less  and  less  evident  as  the  age  of  the  milk  in- 
creases. 

Various  kinds  of  bacteria  may  cause  the  milk  to  taste 
bitter.  Some  of  the  acid  organisms  cause  such  a  change, 
but  more  frequently  the  digesting  bacteria  are  the  source 
of  the  trouble,  and  since  these  are  more  apt  to  develop  in 
pasteurized  milk  than  in  raw,  a  bitter  fermentation  is 


62  Agricultural  Bacteriology. 

more  frequently  noted  in  pasteurized  milk  and  craam 
than  elsewhere.  Low  temperatures  also  favor  the  growth 
of  certain  of  the  types  causing  the  trouble. 

Colored  milk.  Red  milk  is  of  frequent  occurrence 
and  is  most  often  due  to  the  presence  of  blood  which  has 
gained  entrance  to  the  milk  ducts  through  a  wound  in 
the  udder.  The  presence  of  the  blood  can  be  recognized 
with  ease  as  the  red  blood  corpuscles,  that  give  the  blood 
'its  color,  are  heavier  than  the  milk  serum  and  therefore 
settle  to  the  bottom  of  the  milk  receptacle.  "When  the 
color  is  due  to  the  presence  of  blood,  the  milk  will  be  col- 
ored when  it  is  drawn. 

There  are  other  changes  that  may  occur  in  which  a 
reddish  coloration  may  develop,  due  to  the  growtli  of  bac- 
teria. Such  troubles  are  rare  and  have  but  little  eco- 
nomic importance.  Other  pigment-forming  bacteria  oc- 
casionally develop  in  milk  causing  abnormalities  as  to 
color. 

Treatment  of  abnormal  fermentations  in  milk.  If 
the  milk  from  a  dairy  is  constantly  contaminated  with 
bacteria  causing  undesirable  changes  to  such  an  extent  as 
to  injure  the  milk  for  butter  and  cheese,  some  remedial 
measures  must  be  taken.  In  most  cases  a  thorough 
cleaning  of  the  milk  utensils  on  the  farm,  the  cleaning  of 
the  milk-room  and  the  barn,  together  with  the  exclusion 
of  the  cows  from  mud-holes,  ponds  and  creeks  will  suf- 
fice. "When  these  measures  do  not  succeed,  recourse  must 
be  had  to  the  employment  of  disinfectants,  the  use  of 
which  will  be  described  elsewhere. 

The  discovery  of  the  source  from  which  the  harmful 
organisms  come  is  an  important  thing,  for  little  can  be 
done  toward  overcoming  the  defects  until  that  is  known. 


Fermentations  of  Milk.  63 

The  butter  or  cheese  maker,  receiving  milk  from  a  num- 
ber of  farms,  often  finds  it  necessary  to  trace  to  its  source 
on  the  farm  the  abnormal  fermentation  causing  him  trou- 
ble and  loss.  The  test  most  often  used  for  this  purpose 
is  designed  especially  to  detect  the  most  frequent  of  the 
troublesome  fermentations  of  milk,  and  is  known  as  the 
Wisconsin  curd  test.  The  sample  to  be  tested  must  be 
carefully  collected  in  fruit  jars  which  have  been  ster- 
ilized by  boiling,  in  water.  The  various  samples  must 
not  be  taken  by  the  use  of  a  dipper  unless  it  is  sterilized 
before  each  sample  is  taken.  If  this  is  not  done,  the  bac- 
teria remaining  on  the  dipper  may  be  sufficient  to  change 
the  result  in  any  sample  from  what  it  would  have  been, 
in  case  the  sample  had  been  taken  in  such  a  way  as  to 
avoid  such  contamination.  The  best  way  to  take  the 
sample  is  to  fill  the  jar  by  pouring  directly  from  the 
can  of  milk  to  be  tested. 

The  milk  is  warmed  to  98°  F.,  ten  drops  of  rennet 
added,  and  as  soon  as  a  firm  curd  is  formed,  it  is  cut  into 
small  pieces  by  means  of  a  sterile  table  knife.  The  cut- 
ting of  the  curd  allows  the  whey  to  be  expressed.  As  it 
collects  it  is  turned  off  until  the  small  pat  of  curd  is  quite 
dry.  The  jars  are  kept  at  98°-105°  F.  for  ten  to  twelve 
hours.  When  the  curd  forms  most  of  the  bacteria  in  the 
milk  are  caught  in  the  curd,  the  shrinking  of  the  same 
concentrating  the  bacteria  into  about  one-tenth  of  the  vol- 
ume of  the  milk.  They  are  held  in  place  as  in  the  plate 
cultures  described  in  Chapter  II.  They  multiply  rapidly, 
forming  colonies  in  the  curd.  The  jars  are  kept  at  high 
temperatures  in  order  to  favor  the  growth  of  the  unde- 
sirable bacteria.  After  ten  to  twelve  hours  the  curds  are 
examined  as  to  their  texture,  flavor,  and  odor.  A  curd 
which  presents  an  agreeable  acid  odor,  a  close  texture, 


64  Agricultural  Bacteriology. 

few  or  no  gas  holes,  and  no  slimy  condition  is  certain  to- 
have  come  from  a  good  milk.  If  many  gas-forming  bac- 
teria are  present,  the  curd  will  be  filled  with  small  holes, 
and  will  have  a  less  agreeable  odor  than  a  curd  from 
good  milk.  The  greater  the  number  of  gas-forming  bac- 
teria present,  the  more  spongy  is  the  curd  mass.  Some- 
times ill-smelling  curds  are  noted  that  are  not  accom- 
panied by  a  spongy  texture. 

Various  other  abnormal  fermentations  may  be  discov- 
ered by  the  use  of  the  curd  test.  It  may  be  necessary  to- 
make  similar  tests  on  the  milk  of  each  cow  before  the 
source  of  the  trouble  can  be  found. 


CHAPTER  VI. 
RELATION  OF  BACTERIA  TO  BUTTER. 

If  fresh  sweet  milk  is  separated  and  the  cream  churned 
at  once,  a  butter  will  be  obtained  which  has  but  little 
flavor  or  taste.  This  "sweet-cream"  butter  is  used  ex- 
clusively in  France,  Southern  Germany,  and  Italy.  The 
flavor  comes  from  the  milk  itself,  and  is  known  as  the 
primary  flavor  of  butter.  If,  however,  the  same  cream 
is  allowed  to  ferment,  due  to  the  growth  of  the  bacteria 
which  it  contains,  the  butter  will  have  a  much  higher  de- 
gree of  flavor.  Ripened  or  "sour-cream"  butter,  is  the 
type  of  butter  usually  made  in  northern  European  coun- 
tries, England,  and  America. 

The  manufacture  of  sour-cream  butter  undoubtedly 
arose  because  of  its  greater  convenience.  In  making 
sweet-cream  butter,  the  milk  has  to  be  kept  cool  during 
the  time  required  for  creaming  and  the  cream  churned 
daily.  Under  modern  conditions,  by  the  use  of  the  cen- 
trifugal separator,  sweet-cream  butter  can  be  easily 
made,  but  heretofore,  sour-cream  butter  was  easier  to 
make  because  the  cream  could  be  accumulated  in  quan- 
tities and  churned  when  convenient. 

Flavor  of  sour-cream  butter.  In  the  acid  fermenta- 
tion of  milk  and  cream,  not  only  lactic  acid  but  other 
acids  are  produced,  as  well  as  many  other  products,  of 
which  little  or  nothing  is  known.  The  butter  fat  has 
properties  similar  to  other  fats,  one  of  which  is  to  absorb 


66  Agricultural  Bacteriology. 

and  hold  many  substances  having  pronounced  odors  and 
tastes.  In  the  souring  of  cream,  various  products  are 
formed,  some  of  which  are  absorbed  by  the  butter  fat, 
and  give  to  the  sour-cream  butter  its  peculiar  flavor. 
The  lactic  acid  itself  is  of  no  importance  as  far  as  flavor 
production  is  concerned. 

That  the  by-products  of  the  lactic  fermentation  are  the 
important  thing,  and  not  any  change  in  the  fat  during 
the  souring  process  can  be  shown  by  the  fact  that  if 
sweet  cream  is  mixed  with  sour  skim  milk  and  churned  at 
once,  the  butter  will  have  as  much  flavor  as  though  the 
cream  itself  had  been  allowed  to  sour.  This  fact  is  made 
use  of  by  renovated  butter  manufacturers  and  oleomarga- 
rine makers  to  give  taste  and  odor  to  the  tasteless  fats 
they  employ. 

Spontaneous  ripening  of  cream.  All  lactic  acid  bac- 
teria do  not  produce  proper  flavoring  substances.  Those 
which  break  up  the  milk  sugar  with  the  formation  of  gas 
in  the  milk  frequently  impart  an  undesirable  flavor  to 
butter.  Because  of  the  fact  that  clean  pure  milk  us- 
ually undergoes  a  desirable  type  of  fermentation,  the  so 
called  spontaneous  or  natural  ripening  of  cream  gener- 
ally results  in  the  production  of  a  satisfactory  product. 
This  is  the  method  usually  employed  on  farms  and  where 
care  is  taken,  the  best  quality  of  butter  can  often  be  pro- 
duced. The  farm  product  is  not  likely  to  be  as  constant 
in  quality  as  the  factory  butter. 

Home-made  starters.  With  the  advent  of  the  mod- 
ern creamery,  it  became  possible  to  make  a  more  uniform 
product  because  conditions  could  be  more  closely  con- 
trolled. The  most  prominent  factor  in  this  is  the  churn- 
ing at  regular  intervals.  This  should  be  done  when  a 


Relation  of  Bacteria  to  Butter.  67 

proper  amount  of  acid  has  been  developed  in  the  cream. 
As  the  development  of  acid  turns  generally  on  tempera- 
ture conditions  favorable  to  the  growth  of  bacteria  in  the 
cream  uniformity  in  the  ripening  temperature  first  came 
to  be  practiced.  Experience  also  showed  that  the  addi- 
tion of  already  fermented  milk  could  be  advantageously 
employed,  so  gradually  sour  milk  or  butter  milk  began  to 
be  employed.  These  home-made  starters  have  now  long 
been  used  with  success. 

A  recognition  of  the  relation  of  bacteria  to  the  process 
of  cream  ripening  is  comparatively  recent  and  has  re- 
sulted in  much  improvement  in  the  preparation  of  the 
starters  used  in  the  cream.  The  modern  operator  uses 
essentially  the  following  procedure  in  the  preparation  of. 
a  home-made  starter:  a  small  amount  of  milk  which  the 
butter  maker  thinks  has  been  handled  under  clean  con- 
ditions is  allowed  to  sour.  If  the  soured  milk  has  a  de- 
sirable flavor  and  odor,  it  is  added  to  a  larger  quantity 
of  milk  which  has  first  been  heated  to  a  temperature  suf- 
ficiently high  to  kill  the  acid-forming  bacteria  and  which 
has  been  cooled  to  70°-90°  F.  This  mass  of  milk  sours 
quickly  under  the  influence  of  bacterial  growth.  "When 
it  reaches  the  proper  degree  of  acidity,  this  natural 
starter  is  added  to  the  cream,  a  small  amount  being  re- 
served with  which  to  inoculate  a  fresh  quantity  of  heated 
and  cooled  milk.  By  this  process  the  starter  is  propa- 
gated from  day  to  day  and  the  butter  maker  is  able  to 
control  in  large  measure  the  type  of  fermentations  in  the 
cream.  Sooner  or  later  the  starter  propagated  in  this 
manner  becomes  undesirable  in  flavor  and  must  be  re- 
jected. A  new  starter  must  then  be  developed  and 
propagated  as  described. 

The  home-made  starter  has  been  of  great  service  in  .the 


68  Agricultural  Bacteriology. 

development  of  dairying  and  is  still  employed  by  many 
butter  makers.  It  has,  however,  been  gradually  sup- 
planted by  the  pure-culture  or  commercial  starter.  This 
more  recent  advancement  is  due  to  the  discovery  of  the 
Danish  bacteriologist,  Storch,  who  was  the  first  to  show 
the  relation  which  bacteria  hold  to  the  ripening  of  cream. 
Instead-  of  relying  on  natural  fermentations  to  produce 
the  starter,  he  separated,  from  ripened  cream,  the  specific 
organisms  found  therein  and  tested  them  as  to  their 
flavor-producing  properties.  Those  which  were  found  to 
produce  the  most  desirable  flavors  were  then  cultivated 
in  quantities  so  that  they  could  be  distributed  to  the 
creameries. 

The  pure  culture  is  thus  supposed  to  be  a  more  highly 
selected  type  of  the  organism  than  would  be  found  if  re- 
liance was  placed  on  natural  fermentations  alone.  The 
pure  cultures  are  extensively  used  at  the  present  time 
and  aid  in  maintaining  uniform  conditions  in  the  ripen- 
ing of  the  cream  since  the  butter  maker  can  use  the  same 
organism  continuously.  "When  the  starter  propagated 
in  the  creamery  becomes  undesirable  for  use  in  the  cream, 
a  new  pure-culture  starter  is  obtained  from1  the  manu- 
facturer. 

Pasteurization  of  cream  for  butter  making.  The 
cream  to  which  the  pure-culture  starter  is  added  con- 
tains, of  course,  as  does  all  the  milk  and  cream,  lactic 
acid  and  other  organisms  of  various  kinds.  These  nat- 
urally develop  in  the  cream  to  a  greater  or  less  extent 
when  the  pure-culture  starter  is  added  to  raw  cream. 
The  flavor  of  the  butter  is  thus  the  result  of  the  combined 
effect  of  both  the  acid  bacteria  already  present  and  those 
added.  It  was  as  though  grain  had  been  sown  on  an  un- 
plowed  and  weedy  field. 


Relation  of  Bacteria  to  Butter.  69 

The  next  step  in  the  history  of  butter  making,  a  step 
toward  better  control  of  the  flavor  of  the  product,  was  to 
heat  the  cream  to  kill  the  acid  bacteria  already  present 
and  thus,  to  give  a  free  field  to  the  bacteria  in  the  starter. 
The  pasteurization  of  cream  is  a  most  successful  process. 
All  the  butter  made  in  Denmark  is  from  pasteurized 
cream;  much  of  the  butter  made  by  large  creameries  in 
this  country  is  also  treated  in  the  same  way.  It  repre- 
sents the  highest  type  of  modern  butter  making.  The 
cream  is  pasteurized  in  ''continuous  flow"  machines  in 
which  it  is  heated  momentarily  to  170°-190°  F.,  and 
cooled  at  once.  Before  churning  the  cream  must  be 
cooled  to  50°  F.  and  kept  at  this  temperature  for  some 
hours,  otherwise  the  butter  is  apt  to  have  a  soft  and 
mushy  texture. 

Ripened  cream  churns  more  easily  than  does  sweet 
cream  and  the  loss  of  butter  fat  in  the  butter-milk  is  not 
so  great.  This  is  of  considerable  importance  in  cream- 
eries where  the  daily  output  is  several  thousands  of 
pounds. 

Details  of  cream  ripening.  The  cream  should  be 
from  clean  milk  and  allowed  to  sour  at  about  70°-80°  F. 
Pure-culture  starters  have  not  been  extensively  used  on 
the  farm,  but  undoubtedly  they  would  be  of  great  value. 
They  can  be  propagated  in  small  vessels  as  fruit  jars, 
milk  bottles,  etc.  The  details  that  must  be  observed  in 
the  propagation  need  not  be  given  here  as  full  instruc- 
tions accompany  each  pure  culture  sent  out  by  the  manu- 
facturers. 

The  cream  should  be  allowed  to  sour  until  the  acidity 
is  from  0.5-.65  per  cent.  If  the  acidity  is  lower,  the 
flavor  of  the  butter  will  be  very  mild.  If  the  acidity 
increases  to  1  per  cent,  the  flavor  is  apt  to  be  undesirable. 


70  Agricultural  Bacteriology. 

The  poor  quality  of  dairy  butter  is  generally  due  to  the 
fact  that  no  control  is  maintained  over  the  ripening  of 
the  cream,  too  much  acid  usually  being  developed  in  the 
cream. 

Deterioration  of  butter.  Butter  is  in  its  best  condi- 
tion as  soon  as  it  is  churned  and  prepared  for  the  mar- 
ket. Its  best  flavor  is  retained  for  several  days;  the 
period  being  lengthened  by  storage  at  lower  tempera- 
tures. At  summer  temperatures,  the  flavor  becomes  im- 
paired in  the  course  of  a  week  or  so.  The  nature  of  these 
changes  is  very  obscure  and  they  are  designated  usually 
as  "  off  "flavors. 

It  has  been  noted  that  sweet-cream  butter  has  very 
poor  keeping  quality  at  ordinary  temperatures  when 
compared  with  the  sour-cream  product.  This  undoubt- 
edly is  due  to  the  fact  that  many  kinds  of  bacteria  are 
present  in  sweet-cream  butter.  In  sour-cream  butter  the 
majority  of  the  bacteria  are  acid-forming,  most  of  which 
have  no  injurious  effect  on  the  butter.  The  greater  care 
used  in  making  the  butter,  the  better  its  keeping  quality. 
If  it  is  made  from  very  clean  milk,  and  the  cream  soured 
by  pure  cultures,  the  keeping  quality  will  be  excellent. 
It  may  be  further  enhanced  by  pasteurization  of  th& 
cream. 

The  causes  of  the  deterioration  of  the  butter  are  not 
well  known.  It  is  certain  from  what  has  been  said  that 
the  bacteria  must  play  an  important  role,  for  in  no  other 
way  can  the  influence  of  souring  the  cream  and  of  pas- 
teurization be  explained.  The  same  is  also  indicated  by 
the  influence  which  the  water  used"  to  wash  the  butter 
has  on  its  keeping  quality.  If  the  water  is  pure,  as  from 
a  deep  well,  its  influence  will  be  small,  but  if  surface 
water  from  shallow  wells  is  used,  which  contains  many 


Relation  of  Bacteria  to  Butter.  71 

bacteria  coming  from  the  soil,  the  keeping  quality  will  be 
greatly  injured.  This  has  led  to  the  heating  of  the  wash 
water  in  creameries  when  the  supply  is  not  above  ques- 
tion. 

The  changes  which  butter  undergoes  are  usually  ex- 
pressed by  the  word  "rancid."  At  least  two  different 
changes  can  be  distinguished.  The  butter  may  develop 
a  flavor  or  odor  resembling  that  of  tallow.  This  is  due,, 
at  least  in  part,  to  the  action  of  light  and  air  on  the  fat. 
Butter  in  tubs  keeps  better  than  in  small  packages.  The 
true  rancidity,  a  change  in  which  the  butter  acquires  the 
odor  and  taste  of  spoiled  cocoanut  milk  is  due  largely  to 
bacteria. 

The  number  of  bacteria  in  fresh  butter  is  very  large 
but  diminishes  rapidly  after  churning  on  account  of  the 
lack  of  food  and  the  injurious  action  of  the  salt,  which  is 
usually  present  in  such  quantities  as  to  form  a  saturated 
brine  with  the  water  in  the  butter.  The  lactic  acid  bac- 
teria decrease  with  especial  rapidity  while  undoubtedly 
some  other  forms  of  bacteria  and  molds  are  able  to  grow 
in  spite  of  the  salt. 

The  role  of  the  bacteria  in  the  spoiling  of  butter  is 
further  emphasized  by  the  effect  of  cold  storage  on  the 
butter.  In  order  to  preserve*  it,  modern  butter  storage- 
rooms  are  kept  below  zero  Fahrenheit.  After  months  of 
storage,  the  butter  is  unchanged.  It  does,  however,  spoil 
very  quickly  on  being  removed  from  the  cold  room ;  much 
more  quickly  than  before  storage.  Preservatives  are 
widely  used  in  butter,  not  in  our  own  country,  but  in 
Australia  and  NewZealand  in  the  butter  to  be  shipped 
to  England. 

Undesirable  flavors  in  butter.  As  has  been  previ- 
ously mentioned,  the  kind  of  feed  may  influence  the 


72  Agricultural  Bacteriology. 

taste  and  odor  of  the  milk.  The  milk  may  not  have  a 
marked  taste,  while  the  butter  prepared  from  it  may 
show  the  influence  of  the  feed  to  a  great  degree,  because 
the  fat  absorbs  the  flavoring  substances  and  thus  they 
are  concentrated  in  the  butter.  It  is  practically  impos- 
sible to  feed  turnips,  cabbage,  and  rape  without  the  taste 
of  these  vegetables  appearing  in  the  butter.  Green 
clover,  strong  silage,  and  various  weeds  which  the  cattle 
may  eat  when  the  grass  is  short  in  the  pastures  may  also 
injure  the  butter.  Butter  brought  in  contact  with  pro- 
nounced odors,  such  as  that  of  bananas,  will  absorb 
enough  so  that  the  flavor  is  very  evident.  This  absorp- 
tion by  the  fat  may  take  place  either  before  or  after 
churning.  For  this  reason  milk,  cream,  and  butter 
should  be  kept  in  a  place  free  from  all  odors.  Weig- 
mann  of  Germany  has  found  certain  kinds  of  bacteria  in 
milk  which  impart  to  the  butter  a  flavor  like  that  of  tur- 
nips. 

" Fishy"  butter  is  quite  common  causing  in  some 
creameries  a  large  loss.  The  true  cause  of  this  trouble 
is  not  known  with  certainty. 

Moldy  butter.  The  common  molds,  which  appear  so 
quickly  on  bread,  cheese,  etc.,  do  not  as  a  rule  cause  trou- 
ble in  butter  but  certain  other  kinds  of  molds  are  es- 
pecially troublesome.  They  develop  mainly  in  the  outer 
layer  of  the  butter,  where  they  have  access  to  the  oxygen 
of  the  air,  or  on  the  parchment  paper  or  inner  face  of  the 
butter  tub  itself. 


CHAPTER  VII. 
RELATION  OF  BACTERIA  TO  CHEESE. 

Cheese  is  an  important  item  in  the  dietary  of  European 
people.  It  has  a  high  food  value  because  it  represents 
a  concentration  of  three-fourths  of  the  solids  of  the  milk 
to  about  one-tenth  of  their  original  volume.  It  is  also 
largely  used  as  a  condiment.  In  many  European  coun- 
tries the  food  supply  of  a  large  part  of  the  people  is 
coarse  and  relatively  tasteless.  A  small  amount  of  high- 
ly flavored  cheese  renders  such  food  more  appetizing. 

Manufacture  of  cheese.  Cheese  is  made  from  the  fats 
of  the  milk,  the  casein,  certain  ash  constituents,  and  a 
part  of  the  milk  serum.  The  casein  is  curdled  by  allow- 
ing the  milk  to  sour  or  by  the  addition  of  rennet.  The 
curd  holds  the  fat  globules  of  the  milk,  and  when  it 
shrinks  under  the  influence  of  heat  and  acid,  whey  is 
expressed,  leaving  a  mixture  rich  in  fat  and  casein,  and 
containing  from  30  to  50  per  cent  of  milk  serum  or  whey, 
depending  on  the  kind  of  cheese. 

Types  of  cheese.  Cheese  may  be  grouped  into  two 
classes:  (1)  Those  in  which  the  curd  is  obtained  by 
allowing  the  milk  to  sour ;  (2)  those  in  which  the  curd 
is  obtained  by  the  use  of  rennet. 

The  only  important  kind  of  the  first  class  in  this  coun- 
try is  the  cottage  or  Dutch  cheese.  Bacteria  function  in 
the  manufacture  of  this  variety  as  the  curdling  of  the 
casein  is  due  to  the  souring  of  the  milk.  Heating  the 


OF   THE 

UNIVERSITY 


74  Agricultural  Bacteriology. 

milk  also  facilitates  the  coagulation  of  the  curd.  The 
whey  is  removed  from  the  curd  by  straining.  The  cheese 
is  then  salted  and  is  ready  for  use.  Its  flavor  is  that 
of  sour  milk,  or  butter  milk,  as  it  is  really  a  concentrated 
form  of  sour  milk.  It  contains,  of  course,  an  immense- 
number  of  lactic  acid  bacteria.  Cottage  cheese  has  poor 
keeping  qualities,  since  mold  soon  begins  to  grow  on  the 
surface  of  the  moist  mass  of  curd. 

As  representative  of  the  second  group,  the  typical 
American  cheddar  and  the  Swiss  cheese  are  the  best 
known.  In  these  types  the  casein  is  curdled  by  the  ad- 
dition of  rennet  extract,  the  curdling  action  being  de- 
pendent upon  the  coagulating  enzymes  contained  in  this 
animal  extract.  By  cutting  the  curd  mass  and  warming 
the  same,  the  whey  is  rapidly  expressed,  leaving  a  firm 
solid  curd,  which  is  formed  into  various  shapes  by  plac- 
ing the  same  in  moulds.  The  fresh  curd  is  tough,  rub- 
bery, tasteless,  and  practically  insoluble  in  water,  but 
when  placed  under  proper  curing  conditions,  becomes  in 
time,  soft,  plastic,  high  in  flavor,  and  a  large  part  of  it  is 
soluble  in  water.  A  "ripe"  or  cured  cheese  is  easily  di-, 
gested  while  green  cheese  is  indigestible. 

There  are  at  least  four  hundred  different  kinds  of 
cheese,  but  those  which  are  of  importance  in  the  markets 
of  the  world  do  not  exceed  twelve  to  fifteen.  The  re- 
mainder have  merely  a  local  market  in  the  districts 
where  made.  All  varieties  are  produced  from  milk  and 
yet  the  resulting  product  is  far  different.  This  in- 
dicates that  the  conditions  of  manufacture  and  curing 
of  the  product,  directly  or  indirectly,  play  an  important 
part  in  determining  the  type  of  cheese. 

Milk  for  cheese  making.  It  is  very  important  that 
the  milk  for  cheese  shall  be  normal  in  all  respects  and 


lit  lation  of  Bacteria  to  Cheese.  75- 

that  it  shall  not  contain  injurious  kinds  of  bacteria.  As 
will  be  noted  later,  the  lactic  acid  bacteria  are  of  much 
importance  in  the  cheese-making  process.  The  cheese 
maker  can  add  these  organisms  in  the  form  of  a  starter, 
just  as  is  done  in  butter  making.  The  farmer  should 
furnish  to  the  cheese  maker  clean  milk  which  has  been 
kept  cold  so  as  to  prevent  the  growth  of  bacteria  as  far  as 
possible.  If  this  is  done  the  cheese  maker  will  have  little 
trouble,  and  the  product  will  be  good.  '  In  butter  mak- 
ing, fairly  good  butter  can  be  made  from  sour  cream,  or 
even  cream  that  has  an  undesirable  flavor  if  it  is  pasteur- 
ized and  ripened  with  a  proper  starter.  The  cheese 
maker  can  call  no  such  aids  to  his  service.  He  can  con- 
trol in  part  the  course  of  the  changes  that  occur  during 
the  making  process,  but  after  the  cheese  is  made,  he  is 
wellnigh  helpless  so  far  as  the  quality  of  the  cheese  is  in- 
fluenced by  the  milk. 

The  main  duty  of  the  producer  lies  in  the  giving  of 
especial  attention  to  the  washing  of  the  milk  cans  as  these 
utensils  are  generally  employed  for  the  return  of  the 
whey  to  the  farm.  All  of  those  factors  referred  to  under 
the  production  of  clean  and  wholesome  milk  are  here 
equally  applicable. 

Ripening  of  cheese.  The  rennet  which  is  used  to  cur- 
dle the  milk  is  obtained  by  extracting  the  fourth  stomach 
of  calves  that  have  received  no  other  food  than  milk.  It 
can  be  obtained  from  many  other  sources  but  not  so  ad- 
vjantageously.  It  is  prepared  by  the  manufacturers  in 
liquid  or  dry  form.  Formerly  each  cheese  maker  pre- 
pared his  own  rennet  extract  from  the  dried  rennets. 
The  Swiss  maker  still  follows  this  practice.  The  rennet 
extract  contains  the  enzyme,  pepsin,  which  is  found  in 
the  gastric  juice  of  all  kinds  of  animals.  This  enzyme 


76  Agricultural  Bacteriology. 

-acts  only  in  an  acid  medium.  The  reaction  of  the  con- 
tents of  the  normal  stomach  is  acid.  Certain  kinds  of 
.stomach  trouble,  and  indigestion  are  due  to  a  lack  of  acid 
in  the  stomach,  the  food  remains  unacted  upon  by  the 
.stomach  juices,  while  putrefactive  changes  occur  which 
are  marked  by  belching  of  gas  and  offensive  breath. 

The  immense  number  of  lactic  acid  bacteria  that  are 
present  in  the  milk  are  concentrated  in  the  curd  just  as 
are  the  fat  globules  of  the  milk.  In  the  warm  moist  curd 
they  grow  rapidly  and  change  the  sugar  of  the  whey  to 
lactic  acid.  This  acid  enables  the  pepsin  of  the  rennet 
extract  to  act,  changing  the  tough,  rubbery,  insoluble 
curd  to  a  soft  and  partially  soluble  form.  Without  the 
lactic  acid  bacteria  to  produce  this  change  the  cheese  does 
not  ripen.  They  are  absolutely  essential  to  the  ripening 
of  cheese.  Owing  to  the  favorable  growth  conditions, 
during  the  making  and  in  the  first  stages  of  the  ripening 
of  the  cheese,  an  immense  number  of  lactic  acid  bacteria 
are  found  therein.  This  number  rapidly  decreases  with- 
in a  few  days  as  the  sugar  is  soon  completely  fermented, 
and  conditions  are  no  longer  favorable  for  growth. 

Green  cheese  has  none  of  the  flavor  which  a  ripe  cheese 
must  have  in  order  to  make  it  valuable  as  a  commercial 
product.  With  increasing  age  the  flavor  becomes  more 
and  more  marked,  until  it  may  become  so  strong  as  to  be 
undesirable.  The  cause  of  the  typical  flavor  of  cheddar 
or  American  cheese,  as  it  is  often  called,  is  unknown.  It 
has  been  found  that  the  cheese  must  be  made  in  a  certain 
way  and  ripened  under  certain  conditions,  and  unless 
this  is  done  the  product  will  not  have  the  flavor  of  ched- 
dar cheese.  For  example  it  does  not  seem  possible  to 
make  a  cheese  from  pasteurized  milk,  or  to  omit  the  salt- 
ing of  the  curd.  Such  things  strongly  indicate  the  work 
of  bacteria  in  the  formation  of  the  flavoring  substances. 


Relation  of  Bacteria  to  Cheese.  77 

When  the  milk  is  clean  and  a  pure-culture  starter  is 
used  the  cheese  is  generally  of  good  quality.  If  the  milk 
is  dirty,  because  of  careless  methods  on  the  farm,  a  large 
number  of  gas-forming  bacteria  will  be  present.  These 
grow  in  the  curd  together  with  the  lactic  acid  bacteria, 
causing  the  curd  to  be  filled  with  holes  due  to  the  impris- 
oned gas,  and  greatly  injuring  the  flavor  of  the  cheese. 
The  greatest  trouble  with  which  the  cheese  maker  has  to 
contend  is  gassy  milk.  Milk  of  this  nature  can  be  de- 
tected by  the  use  of  the  Wisconsin  curd  test  (p.  63). 

Other  kinds  of  bacteria  than  the  gas-forming  types 
may  also  injure  the  cheese.  If  the  acid-forming  bacteria 
do  not  grow  quickly  in  the  milk,  putrefactive  organisms 
may  develop  and  cause  offensive  odors.  In  case  of  some 
of  the  foreign  types,  the  cheese  may  change  from  a  firm 
to  a  soft,  slimy  mass  which  has  a  most  offensive  odor  and 
bitter  taste.  The  putrefactive  bacteria  can  not  develop 
in  a  normal  cheese  because  of  its  acid  reaction.  Chro- 
mogenic  bacteria  may  grow  in  the  milk  and  cheese  and 
produce  colored  spots  in  the  cheese.  A  trouble  met  with 
in  Canada  and  New  York  is  called  the  ' '  rusty  spot. ' '  It 
does  not  injure  the  taste  of  the  product,  but  causes  it  to 
have  a  strange  and  unappetizing  appearance  and  of 
course  lowers  its  commercial  value. 

Foreign  types  of  cheese.  There  are  on  the  American 
markets  many  types  of  cheese  that  have  been  imported 
from  the  countries  to  which  they  are  peculiar.  Among 
the  most  important  of  these  are  the  Swiss  cheese  or  Em- 
menthaler,  made  in  Switzerland,  Roquefort  from  France, 
Gorgonzola  from  Italy,  Stilton  from  England,  Lim- 
burger  from  Germany,  and  Camembert  and  Brie  from 
France.  Because  of  the  high  price  that  these  cheese 


78  Agricultural  Bacteriology. 

bring,  efforts  have  been  made  to  manuf a.cture  them  in 
America.  The  greatest  degree  of  success  is  met  in  the 
making  of  Swiss  and  Limburger.  Many  millions  of - 
pounds  of  these  cheese  are  made  annually  in  Wisconsin. 
Camembert  is  made  to  a  small  extent  in  some  of  the  east- 
ern states.  The  manufacture  of  the  remaining  kinds  has 
not  yet  been  put  on  a  commercial  basis  in  this  country. 

Swiss  cheese.  This  cheese  is  made  from  very  sweet 
milk.  It  is  especially  important  that  the  milk  be  pro- 
duced under  such  conditions  as  to  prevent  contamination 
with  gas-forming  bacteria,  since  the  Swiss  maker  can  not 
make  use  of  the  means  available  to  the  cheddar  maker  to 
prevent  and  overcome  these  forms.  The  Swiss  makers 
fear  gassy  milk  very  much ;  they  insist  that  the  farmers 
•shall  not  include  in  the  milk  brought  to  the  factory  that 
drawn  from  a  cow  suffering  from  garget  since  they  think 
that  such  milk  will  cause  gas  in  the  cheese.  The  Swiss 
maker  insists  that  the  farmer  shall  not  strain  his  milk. 
The  milk  is  strained  at  the  factory.  By  watching  the  ap- 
pearance of  the  strainer  the  maker  can  detect  dirt  in  the 
milk  and  often  cases  of  udder  trouble  in  the  herds  of  the 
patrons.  He  thus  knows  better  the  conditions  under 
which  the  milk  was  produced  than  does  the  cheddar 
maker  whose  patrons  strain  the  milk  on  the  farm. 

Rennet  and  the  lactic  acid  bacteria  play  the  same  part 
in  the  ripening  of  Swiss  cheese  that  they  do  in  cheddar, 
but  as  the  flavor  is  different  the  causes  operative  here 
must  be  other  than  in  cheddar  cheese.  Swiss  cheese 
does  not  have  the  solid  texture  of  cheddar  cheese  but  is 
studded  with  holes  from  the  size  of  a  hazelnut  to  a  hick- 
orynut.  These  holes  are  called  ' '  eyes ' '  and  a  cheese  that 
lacks  them  is  termed  a  "blind"  cheese.  As  these  open- 
ings exist  in  a  normal  cheese  they  may  be  called  the  trade 


Relation  of  Bacteria  to  Cheese.  79 

mark  of  this  type  of  cheese.  They  are  of  commercial 
value  since  a  cheese  that  lacks  them  will  not  sell  for  as 
much  as  one  of  similar  flavor  and  texture  containing  the 
eyes.  At  the  time  when  the  cheese  is  supposed  to  be  at 
its  best,  the  eyes  often  contain  a  clear  brine  which  is 
termed  "tears."  The  eyes  are  caused  by  bacteria  that 
change  a  portion  of  the  lactic  acid  to  propionic  and 
acetic  acids.  Carbon  dioxide  is  also  produced.  This 
gas  produces  the  holes.  The  change  of  the  lactic  acid  to 
other  acids  undoubtedly  influences  the  flavor  of  the 
cheese. 

Roquefort,  Gorgonzola,  and  Stilton  cheese.  There 
are  three  kinds  of  cheese  found  in  the  world's  markets 
that  are  very  peculiar  as  to  the  manner  of  ripening. 
These  cheese  are  Roquefort,  Gorgonzola  and  Stilton. 
The  first  is  made  in  France  from  sheep 's  milk,  the  others 
are  made  from  cows'  milk.  These  cheese  are  luxuries, 
selling  for  fifty  to  seventy -five  cents  a  pound. 

The  rennet  and  lactic  acid  bacteria  play  the  same  role 
in  the  manufacture  and  ripening  of  these  cheese  as  in 
the  cheddar  cheese.  One  of  the  causes  of  the  peculiar 
flavor  of  these  cheese  is  a  mold  very  similar  to  the  ordi- 
nary blue-green  bread  mold.  In  the  making  of  Roque- 
fort cheese,  the  curd  when  put  to  press  is  sprinkled  with 
bread  crumbs  upon  which  the  mold  is  growing.  This 
mold  like  all  others  can  grow  only  in  the  air,  and  in  order 
to  allow  the  air  to  penetrate  into  the  cheese,  it  is  pierced 
full  of  small  holes  by  means  of  slender  needles.  The 
mold  grows  and  forms  its  greenish  spores,  giving  to  the 
-cheese,  when  cut,  the  appearance  of  green  and  white 
marble.  The  flavor  is  characteristic  and  is  produced 
only  when  the  mold  is  present. 

Gorgonzola  and  Stilton  cheese  contain  the  same  mold 


80  Agricultural  Bacteriology. 

and  present  the  same  appearance.  The  mold  is  not 
added  intentionally,  the  maker  relying  on  a  sufficient 
seeding  of  the  curd  from  the  utensils,  etc. 

Limburger  and  Camembert  cheese.  The  cheddar  and 
Swiss  cheese  are  typical  examples  of  the  so  called  ' '  hard ' ' 
cheese.  Limburger  and  Camembert  are  "soft"  cheese. 
The  soft  varieties  are  always  prepared  in  small  molds, 
since  it  would  be  impossible  to  handle  them  if  they  were 
large,  and  also  the  proper  ripening  process  proceeds  from 
the  outer  layers  toward  the  inside.  A  cheddar  cheese 
can  be  made  of  any  size  desired;  a  large  one  ripens  as 
well  as  a  small  one  since  the  process  goes  on  uniformly 
throughout  the  entire  mass  of  the  cheese.  Swiss  cheese- 
ripen  in  the  same  manner  but  they  are  always  made  with 
a  large  surface  compared  to  the  volume  of  the  cheese  on 
account  of  the  method  of  salting.  The  salt  is  applied  to 
the  surface  of  the  cheese. 

The  soft  cheese  will  keep  but  a  short  time  while  many 
of  the  hard  types  will  keep  for  years.  The  most  impor- 
tant of  the  soft  cheese  are  Limburger,  Camembert,  and 
Brie.  In  all  of  these  the  rennet  and  lactic  acid  bacteria 
play  the  same  part  in  the  ripening  process  as  they  do  in 
cheddar  and  Swiss  cheese.  Again,  as  in  Roquefort, 
molds  are  one  of  the  factors  in  ripening  and  in  flavor  pro- 
duction. In  the  case  of  Camembert  and  Brie  the  mold 
growth  is  confined  to  the  outside  of  the  cheese,  instead  of 
growing  through  the  cheese.  The  mold  instead  of  pro- 
ducing colored  spores  as  in  Roquefort  is  white.  At  least 
two  molds  are  necessary  for  the  development  of  the  typi- 
cal flavor,  one  the  common  mold  of  milk,  Oidium  lactis 
which  forms  a  white  velvet-like  growth  on  the  surface  of 
sour  milk,  the  other  a  white  mold  closely  related  to  the 
mold  found  in  Roquefort  cheese.  The  cheese  are  not 


Relation  of  Bacteria  to  Cheese.  81 

usually  inoculated  with  the  molds  as  the  accidental  infec- 
tion in  old  factories  is  sufficient.  Even  under  the  best  of 
conditions  many  cheese  do  not  produce  a  typical  flavor 
and  must  be  sold  at  a  low  price. 

As  stated  the  ripening  of  these  cheese  gradually  passes 
from  the  outside  to  the  inside.  When  the  influence  of 
the  mold  has  penetrated  to  the  center  of  the  cheese  the 
ripening  is  completed.  The  cheese  then  begins  to  de- 
teriorate. If  the  cheese  is  too  large,  the  outer  layer  be- 
comes overripe  before  the  inner  part  is  ripe. 

Limburger  cheese  is  similar  to  Camembert  and  Brie  in 
that  the  ripening  process  begins  on  the  outside  of  the 
cheese.  The  kinds  of  bacteria  and  molds  that  are  essen- 
tial are  not  well  known.  A  reddish-brown  layer  of  mold 
and  bacterial  growth  develops  on  the  surface.  The  ac- 
tion of  this  mass  of  growth  gradually  penetrates  into  the 
cheese,  changing  the  color  of  the  curd  from  a  white  to  a 
translucent  yellow.  The  typical  flavor  is  connected  with 
the  growth  of  these  organisms. 


CHAPTER  VIII. 
RELATION  OF  BACTERIA  TO  MARKET  MILK. 

The  demands  of  the  cities  for  an  increased  milk  supply 
are  constantly  more  pressing.  Each  year  the  zone  from 
which  they  draw  their  supply  is  widened,  until  in  some 
cases  it  extends  for  hundreds  of  miles.  The  milk  trains 
for  New  York  start  from  the  St.  Lawrence  valley  over 
two  hundred  miles  away.  In  the  winter  the  milk  zone  of 
New  York  city  is  extended  much  farther,  milk  and  cream 
being  shipped  from  Ohio.  In  Europe,  progressive  Den- 
mark has  exported  milk,  supplying  in  considerable  quan- 
tities milk  to  the  Berlin  market. 

Not  only. is  there  a  steady  increase  in  the  amount  of 
milk  needed,  but  as  public  opinion  becomes  more  intelli- 
gent there  is  a  growing  demand  for  an  improvement  in 
quality  as  well.  It  is  becoming  more  thoroughly  recog- 
nized that  many  of  the  infantile  diseases  are  dependent 
upon  the  quality  of  the  milk  supply.  Consequently,  city 
boards  of  health  are  increasing  the  rigidity  of  their  in- 
spection service.  "What  the  cities  want  is  pure  milk 
drawn  under  clean  conditions  from  healthy  cows,  and 
handled  in  a  sanitary  manner. 

In  the  city  of  two  decades  ago,  and  in  the  small  city 
and  town  of  today,  the  milk  is  largely  peddled  on  the 
streets  by  the  farmer. 

There 'is  then  a  direct  contact  between  the  producer 
and  consumer.  The  latter  can  easily  find  how  the  milk 


Relation  of  Bacteria  to  Market  Milk.  83 

he  consumes  is  handled  if  he  desires  to  do  so.  The  ap- 
pearance of  the  wagon  and  the  delivery  man  is  certain  to 
mirror  quite  accurately  the  condition  on  the  farm  with 
reference  to  cleanliness.  With  milk  purchased  from  a 
dealer,  with  the  farm  many  miles  away,  the  consumer 
cannot,  even  if  he  wishes  to  do  so,  determine  the  condi- 
tions at  the  point  of  production.  The  city  has  had  to 
step  in  and  see  that  its  people  are  receiving  clean  and 
healthful  milk. 

City  regulations.  Each  city  has  met  the  problem  in 
its  own  way.  The  city  health  department  establishes 
rules  to  which  every  farmer  must  conform  if  he  wishes 
to  sell  milk  in  the  city.  In  order  to  determine  whether 
the  producer  does  meet  the  conditions  imposed,  the  farms 
are  inspected  by  a  representative  of  the  health  depart- 
ment. Certain  standards  are  established  and  the  farm 
inspection  is  supplemented  by  tests  made  in  the  labora- 
tory. The  city  often  demands  that  the  milk  shall  not 
contain  more  than  a  certain  number  of  bacteria  (for  ex- 
ample 500,000  or  1,000,000  per  cubic  centimeter)  and 
milk  containing  a  greater  number  is  looked  upon  as  un- 
lawful milk.  The  milk  of  the  farmer  who  does  not  con- 
form to  the  rules  is  returned  to  him  or  is  confiscated  by 
the  -city.. 

Certified  milk.  Some  cities  allow  various  grades  of 
milk  to  be  sold  and  prescribe  the  methods  that  shall  be 
used  in  the  production  of  them.  One  grade  of  milk  to 
which  a  great  deal  of  attention  has  been  attracted  in  the 
last  few  years  is  that  known  as  certified  milk.  Physi- 
cians are  desirous  of  having  a  supply  that  they  can  rec- 
ommend for  the  feeding  of  children.  The  medical  socie- 
ties have  appointed  a  commission  which  draws  up  regu- 


84  Agricultural  Bacteriology. 

lations  to  which  each  farmer  must  conform  who  desires 
to  have  his  milk  certified  by  the  commission.  The  com- 
mission employ  experts  to  aid  in  seeing  that  the  rules  are 
followed  by  the  producers.  A  physician  examines  the 
attendants  on  the  farm  as  to  presence  of  contagious  dis- 
eases and  makes  a  general  sanitary  examination  of  the 
premises;  a  veterinarian  examines  the  cows  as  to  their 
health  and  applies  the  tuberculin  test  to  the  entire  herd 
at  frequent  intervals ;  a  bacteriologist  examines  the  milk 
for  numbers  of  bacteria  and  a  chemist  determines  the 
amount  of  fat,  milk  solids,  etc.  These  examinations  act 
as  a  most  efficient  check  on  the  methods  followed  on  the 
farm  since  if  any  of  the  processes  in  the  production  and 
handling  of  the  milk  are  slighted,  it  is  certain  to  show 
in  an  increased  number  of  bacteria. 

The  rules  of  the  commission  are  usually  very  strict, 
giving  in  detail  how  the  cows  shall  be  cleaned  and  fed, 
how  the  stable  shall  be  kept,  the  feed  that  can  be  used, 
the  care  and  nature  of  the  utensils,  the  handling  of  the 
milk,  the  toilet,  and  dress  of  the  milkers.  The  number  of 
bacteria  allowed  in  certified  milk  is  usually  10,000  per 
cubic  centimeter.  It  requires  the  greatest  attention  to 
details  of  cleanliness  to  produce  such  milk.  Certified 
milk  sells  from  fifteen  to  thirty  cents  a  quart.  It  is  thus 
out  of  reach  of  the  great  mass  of  the  people. 

General  improvement  of  milk  supplies.  There  is  a 
rapidly  growing  demand  on  the  part  of  the  general  pub- 
lic that  improvement  in  the  general  milk  supplies  should 
be  made  and  the  experience  of  practical  dairymen  has 
shown  that  clean,  wholesome  milk  can  be  produced  at  a 
trifling  additional  expense,  and  that  this  clean  milk,  for 
all  practical  purposes,  is  as  good  as  the  much  more  ex- 
pensive certified  product.  The  cows,  the  feed,  the  milk- 


Relation  of  Bacteria  to  Market  Milk.  85 

ing,  and  the  delivery  of  the  milk,  need  cost  but  a  little 
more  than  is  necessary  in  the  production  of  the  poorest 
grade  of  milk.  A  slight  amount  of  labor  applied  at  im- 
portant points  is  the  necessary  thing.  A  stable  that  can 
be  kept  clean  and  so  arranged  that  the  cows  can  not  get 
dirty,  a  little  time  expended  in  cleaning  the  animals  pre- 
paratory to  milking,  judgment  in  the  time  of  feeding, 
the  use  of  a  small  topped  pail,  rapid  and  thorough  cool- 
ing of  the  milk  in  a  clean,  well  ventilated  milk  room,  and 
storage  in  clean  cans  will  enable  any  farmer  to  produce 
milk  that  will  be  as  healthful  and  almost  as  desirable  in 
every  way  as  that  which  must  be  sold  at  a  much  higher 
price.  It  has  been  estimated  that  with  a  herd  of  ten 
cows  producing  one  hundred  quarts  of  milk  per  day  that 
the  additional  labor  and  expense  necessary  to  produce 
clean,  healthful  milk  need  not  amount  to  more  than  one- 
fourth  of  a  cent  per  quart.  With  larger  herds  it  will  be 
less. 

The  highest  grade  of  milk  is  a  luxury,  a  very  desirable 
one  to  be  sure,  but  one  that  the  mass  of  people  must  pass 
by.  Efforts  must  be  directed  to  the  production  of  a  milk 
that  shall  be  clean  and  healthful,  that  can  be  sold  at  a 
price  within  the  reach  of  the  people  and  still  give  to  the 
farmer  an  equitable  return  for  his  labor  and  interest  on 
his  capital. 

City  regulation  of  milk  supplies.  The  control  of  cit- 
ies over  their  milk  supplies  can  not  be  better  illustrated 
than  by  reproducing  the  rules  adopted  by  the  Chicago 
Board  of  Health  with  reference  to  the  handling  of  the 
milk  on  the  farm.  At  first  these  rules  may  seem  compli- 
cated and  cumbersome,  but  it  will  be  noted  that  they 
contain  nothing  that  is  not  essential  to  the  production  of 
good  milk. 


86  Agricultural  Bacteriology. 

Unclean  milk  not  to  enter  the  city  of  Chicago.  All 
milk  entering  the  city  of  Chicago  and  all  milk  sold,  of- 
fered for  sale,  or  received  with  the  intention  of  selling  or 
offering  for  sale  must  be  clean,  wholesome  and  uninfected 
with  disease  germs  or  anything  liable  to  convey  and 
transmit  disease. 

Unclean  milk — Defined.  All  milk  produced  on  farms 
or  prepared,  handled  or  otherwise  treated  on  the  prem- 
ises or  in  places  where  the  rules  of  the  department  are 
violated  shall  be  declared  unclean,  unwholesome  and  in- 
fected. The  sale  of  or  offering  for  sale  of  such  milk  is 
prohibited. 

Unclean  milk  condemned.  All  unclean,  unwhole- 
some or  infected  milk  shall  be  condemned  for  human 
food.  Such  milk  shall  be  returned  to  the  producer  and 
tagged  with  the  "Department  Condemned"  tag  and  con- 
demnation slip  shall  be  mailed  to  the  shipper  at  once ;  if, 
following  this,  the  said  producer  or  shipper  again  sends, 
into  the  city  unclean,  unwholesome  or  infected  milk,  the 
same  shall  be  condemned  and  rendered  unfit  for  human 
food,  by  coloring  or  otherwise  treating,  or  shall  be  poured 
into  the  sewer. 

Condition  and  care  of  cows.  The  cows  must  be 
healthy  and  free  from  tuberculosis.  If  an  examination 
by  the  dairy  inspector  shows  evidence  of  excessive  ema- 
ciation, glandular  enlargement,  nodular  formations,  mas- 
titis, tumor,  recent  parturition,  cough,  dyspnoea,  fever, 
pneumonia,  exhaustion,  lock  jaw,  black  leg,  anthrax, 
hemorrhagic  septicemia,  or  any  other  infectious  disease, 
or  any  evidence  of  tuberculosis,  the  milk  of  the  herd  shall 
be  declared  infected  until  the  unhealthy  cow  or  cows 
have  been  removed  and  until  an  acceptable  statement 


Relation  of  Bacteria  to  Market  Milk.  87 

from  a  recognized,  licensed  veterinarian  or  regular  dairy 
inspector  is  filed  with  the  Milk  Division,  showing  that 
such  suspicious  cow  or  cows  are  free  from  infectious  dis- 
ease. Milk  from  cows  reacting  to  tuberculin  shall  be  re- 
jected unless  it  shall  have  first  been  pasteurized  at  a  tem- 
perature of  170°  F.  or  over  for  thirty  seconds  or  longer  in 
a  stream  not  less  than  a  quarter  of  an  inch  thick.  Milk 
from  cows  fifteen  days  before  and  one  week  after  calving 
shall  be  rejected.  Cows  must  be  kept  as  clean  as  possible 
on  flanks,  belly,  udder,  and  tail.  Long  hair  must  be 
clipped  from  the  udder  and  sufficiently  from  the  tail  to 
clear  the  ground.  The  feeding  of  slops,  refuse  of  any 
distillery  or  brewery,  glucose  or  any  malt  and  ensilage 
that  has  been  subject  to  fermentation,  putrefaction  or  de- 
composition is  prohibited.  Pure  water  in  sufficient 
quantities  must  be  at  hand  at  all  times.  The  cows  must 
not  be  overheated  by  hard  driving,  nor  be  allowed  to- 
stand  in  mud  holes,  dirty  sloughs  or  ditches.  Mud  holesr 
dirty  sloughs  and  ditches  shall  not  be  allowed  to  exist  in 
the  pastures  or  cow  yards  where  cows  for  the  production 
of  milk  are  kept. 

Condition  of  barnyard.  The  barnyard  or  cow  barn 
must  be  kept  reasonably  clean  and  free  from  mud,  soft 
manure  and  must  be  well  drained.  Piles  and  heaps  of 
manure  shall  not  be  less  than  twenty-five  feet  away  from 
any  stable  door  or  window  between  December  first  and 
April  first  and  not  less  than  three  hundred  feet  away 
during  the  other  months  of  the  year. 

Stable.  The  floors  must  be  tight,  preferably  con- 
structed of  cement,  and  free  from  defects.  The  ceilings 
should  be  tight  if  a  storage  loft  is  kept  above.  The  walls 
should  be  whitewashed  every  spring  and  fall  and  kept 


88  Agricultural  Bacteriology. 

•clean  at  all  times.  Each  cow  must  have  at  least  four 
hundred  cubic  feet  of  air  space  and  there  must  be  ample 
provision  for  movement  of  air  and  ventilation,  so  that 
the  air  never  gets  foul.  At  least  two  square  feet  of  un- 
obstructed window  glass  space  shall  be  provided  for  each 
cow.  Soiled  bedding  must  be  removed  daily  and  the 
manure  must  be  removed  from  the  stalls  and  open  ma- 
nure gutters  twice  a  day.  All  bedding,  removing  of 
manure,  sweeping  and  cleaning  of  mangers  must  be  done 
.at  least  one-half  hour  before  milking.  The  stable  must 
Jbe  reasonably  free  from  flies. 

Cats  and  dogs  must  not  be  permitted  in  the  stable. 

Milkers.  Milkers  should  neither  have  nor  come  in 
contact  with  contagious  diseases.  Should  any  case  of 
communicable  disease  such  as  typhoid  fever,  smallpox, 
scarlet  fever,  diphtheria,  measles,  or  chicken  pox  occur 
on  the  dairy  farm  among  the  milkers  or  their  families, 
the  Division  of  Milk  Inspection  must  be  promptly  noti- 
fied. 

Milking.  Before  each  milking  the  udder  should  be 
wiped  with  a  clean,  damp  cloth  or  washed  with  soap  and 
water,  if  necessary.  The  hands  should  be  washed  before 
starting  to  milk  and  again  well  dried  with  a  clean  towel. 
The  hands  and  teats  should  be  kept  dry  during  the  milk- 
ing. If  they  become  moistened  with  milk  they  should  be 
wiped  dry  with  a  clean  towel.  Suitable  clean  outer  gar- 
ments, such  as  overalls  and  jumpers,  should  be  put  on 
before  milking.  The  milk  stool  must  be  clean.  Milking 
should  be  done  regularly,  having  the  periods  of  as  nearly 
equal  length  as  possible.  The  first  few  streams  from 
each  teat  should  be  rejected.  The  first  half  of  the  milk 
given  should  not  be  separated  from  the  latter  half  or 


Relation  of  Bacteria  to  Market  Milk.  89 

strappings  and  be  sold  separately.  The  top  of  the  milk 
pail  should  be  as  small  as  possible,  not  larger  than  six  or 
eight  inches,  to  keep  out  dirt,  and  if  anything  falls  in  the 
milk,  such  as  straw  or  manure,  then  the  milk  should  be 
rejected.  The  milk  from  each  cow  should  be  removed 
from  the  stable  immediately  after  it  is  obtained. 

Milk  cans  and  utensils.  All  utensils  used  in  the  pro- 
duction and  shipping  of  milk,  such  as  cans,  covers,  bot- 
tles, dippers,  skimmers,  measures,  strainers,  stirrers,  etc., 
must  be  so  constructed  that  all  parts  are  absolutely  free 
from  places  where  milk  can  accumulate  or  soak  in,  so 
that  it  cannot  be  removed  by  simple  washing.  The  sur- 
face coming  in  contact  with  milk  and  cream  must  be 
smooth  and  free  from  excessive  rust.  All  utensils  in- 
cluding cans  must  be  kept  scrupulously  clean,  inside  and 
outside,  at  all  times.  They  should  be  cleansed  by  wash- 
ing with  a  brush  and  soap)  or  washing  powder  and  hot 
water  and  thorough  rinsing.  After  this  cleansing  they 
should  be  sterilized  with  boiling  water  and  then  kept  in- 
verted in  a  place  free  from  dust  and  flies.  Strainers, 
whether  metal,  gauze  or  cotton  must  be  absolutely  clean 
when  used  for  the  straining  of  milk.  Milk  cans  should 
be  used  for  no  other  purpose.  Bottle  caps  must  be  kept 
in  clean,  covered,  dry  and  dust  proof  receptacles.  All 
cans  and  utensils  must  be  free  from  defects  and  rough  or 
uneven  surfaces. 

Care  of  milk  on  the  dairy  farm.  The  room  where 
utensils,  milk  pails,  strainers  and  the  milk  are  kept 
should  be  separated  from  both  the  house  and  the  stable 
and  be  used  only  for  dairy  purposes.  It  should  be  kept 
neat,  clean,  well  ventilated  and  free  from  flies  and  dust. 
No  odds  and  ends  or  other  unnecessary  things  should  be 


90  Agricultural  Bacteriology. 

stored  in  the  milk  room.     The  milk  room  must  be  free 
from  odor. 

Milk  should  be  strained  through  a  piece  of  clean  linen 
or  cotton,  then  it  should  be  rapidly  cooled  to  50°  F. 
within  two  hours  after  milking  and  kept  below  that  tem- 
perature until  delivery.  The  evening  milk  must  not  be 
mixed  with  the  morning  milk  and  old  milk  must  not  be 
mixed  with  the  fresh.  The  cans  must  be  tightly  closed 
when  kept  in  the  cooler  and  sealed  when  hauled  to  the 
milk  platform.  During  this  transportation  they  must 
bo  covered  and  protected  from  the  heat.  This  is  best  ac- 
complished by  carrying  in  a  covered  spring  wagon.  Cans 
should  never  be  delivered  too  early  to  the  milk  platform. 
They  should  be  covered  with  a  damp  cloth  in  the  warm, 
weather  while  standing  there. 

Water  supply.  The  water  supply  on  the  farm  must 
be  ample  and  free  from  any  danger  of  pollution  with  ani- 
mal matter  or  refuse.  Water  used  for  the  washing  of 
cans  and  utensils  must  be  free  from  all  nitrites  and  not 
contain  more  than  nine  thousandths  of  one  part  of  free- 
ammonia  and  nine  thousandths  of  one  part  of  albuminoid 
ammonia  in  one  hundred  thousand  parts.  It  must  not 
contain  more  than  one  thousand  bacteria  per  cubic  cen- 
timeter and  be  free  from  pathogenic  bacteria,  including 
colon  bacilli.  Water  from  sloughs,  ponds,  ditches  or 
other  sources  subject  to  contamination  must  never  be 
used  for  the  washing  of  cans  or  utensils.  When  typhoid 
fever  occurs  the  use  of  the  water  on  the  farm  must  be 
discontinued  for  the  washing  of  cans  and  utensils  until 
it  has  been  passed  upon  by  the  Director  of  the  Labora- 
tory of  the  Department  of  Health. 

Sanitary  standard  for  milk.  All  milk  sold,  offered' 
for  sale,  kept  with  the  intention  of  selling,  or  sent  to  the 


Relation  of  Bacteria  to  Market  Milk.  91 

city  for  the  purpose  of  selling  must  be  free  from  dirtr 
foreign  material,  and  sediment.  Not  more  than  a  per- 
ceptible sediment  shall  be  left  on  a  piece  of  white  linen 
cloth  four  inches  square  when  a  quart  of  well  mixed  milk 
is  strained  through  it.  Milk  on  arrival  in  the  city  must 
not  contain  more  than  one  million  bacteria  per  cubic 
centimeter  from  May  first  to  September  thirtieth  and  not 
over  five  hundred  thousand  per  cubic  centimeter  between 
October  first  and  April  thirtieth.  Milk  for  delivery  to 
the  consumer  shall  not  contain  an  excessive  number  of 
bacteria.  The  sale  of  milk  containing  over  three  million 
bacteria  per  cubic  centimeter  is  prohibited  and  the  dealer 
selling  or  offering  for  sale  such  milk  shall,  after  three  ex- 
aminations of  his  milk  by  the  bacteriologist  and  showing 
bacterial  counts  above  three  million  be  prohibited  from 
selling  milk  until  the  method  of  production  and  handling 
of  his  milk  supply  has  been  properly  regulated  by  the  de- 
partment. The  sale  of  -milk  containing  tubercle,  ty- 
phoid, diphtheria,  and  other  pathogenic  bacteria  is  pro- 
hibited. The  sale  of  milk  containing  excessive  numbers 
of  putrefactive  and  gas-producing  micro-organisms  is 
prohibited. 


SECTION  III. 
RELATION  OF  BACTERIA  TO  DISEASE. 


CHAPTER  IX. 
TRANSMISSIBLE  DISEASES. 

Bacteria  are  classified  according  to  their  manner  of  nu- 
trition into  saprophytes  and  parasites.  The  saprophytic 
forms  live  on  dead  organic  matter,  the  parasites  live  in 
the  bodies  of  other  living  forms  which  may  be  either 
plants  or  animals.  The  form  affected  is  known  as  the 
host,  and  the  invading  organism  as  the  parasite.  There 
are  many  forms  of  bacteria  that  may  live  in  the  animal 
body  and  cause  no  disturbance.  Still  other  forms, 
known  as  pathogenic  or  disease-producing  organisms,  by 
their  growth  in  the  body  of  an  animal  cause  changes  that 
may  injure  the  body  or  cause  the  death  of  the  animal  it- 
«elf. 

Transmissible  diseases.  Diseases  traceable  to  such 
causes  are  capable  of  being  communicated  from  one  sus- 
ceptible host  to  another,  and  are  known  as  transmissible 
or  communicable  diseases.  Many  forms  of  disease  are 
the  result  of  some  physiological  disturbance  of  the  body 
such  as  poor  digestion,  circulation,  etc.  These  are  not 
transmissible  and  no  danger  of  spread  from  one  animal 
to  another  exists.  All  transmissible  diseases  are  caused 
by  the  infection  of  the  proper  host  with  the  parasite,  and 
~by  the  growth  of  the  parasite.  In  order  that  infection 


Transmissible  Diseases.  9$ 

of  a  second  host  may  occur  the  parasite  must  escape  from 
the  body  of  the  first  in  some  manner.  The  parasitic  bac- 
teria can  not,  as  a  rule,  readily  multiply  outside  the  body 
of  the  proper  host.  The  opportunity  for  direct  trans- 
mission from  the  sick  animal  to  another  healthy  one  is 
always  so  great  that  the  infection  is  apt  to  be  spread  in 
this  immediate  way.  Even  where  direct  transmission 
from  the  one  animal  to  another  does  not  occur,  the  escape 
of  the  causal  parasite  into  the  outside  environment  per- 
mits of  indirect  infection  through  accidental  contamina- 
tion of  water,  food  and  other  objects. 

Each  disease  is  caused  by  a  specific  organism.  No 
other  organism  can  cause  the  disease  and  without  the 
proper  organism  the  disease  is  impossible.  Each  case  of 
the  disease  thus  demands  a  previous  case.  Sometimes 
the  relation  between  the  two  is  easily  established,  often  it 
can  not  be  traced.  In  order  to  prevent  or  treat  any 
transmissible  disease,  it  is  of  advantage  to  know  the  cause 
of  the  disease,  the  nature  of  the  causal  organism,  the  way 
in  which  it  enters  the  body  of  the  animal,  the  portions  of 
the  body  in  which  it  grows,  the  changes  it  produces,  and 
lastly,  the  ways  in  which  it  leaves  the  body  of  the  affected 
animal.  Unless  these  things  are  known,  many  things 
will  be  left  undone  that  are  necessary  to  prevent  the 
spread  of  the  disease.  Often  many  things  are  done 
which  have  no  importance  in  preventing  the  spread  of 
the  trouble. 

Portals  of  entrance  of  bacteria.  The  bacteria  enter 
the  body  of  the  animal  in  a  number  of  ways.  The  skin 
acts  as  a  protective  layer  to  the  body  proper,  and  as  long 
as  it  is  intact  prevents  the  entrance  of  bacteria  into  the 
body.  As  soon  as  it  is  cut,  punctured  or  bruised,  oppor- 
tunity is  offered  for  the  entrance  of  bacteria.  These  are 


94  Agricultural  Bacteriology. 

most  frequently  introduced  into  wounds  with  the  dirt  at 
the  time  the  wound  is  made.  A  wound  that  does  not 
bleed  freely,  or  one  that  is  not  cleaned  thoroughly,  is 
more  likely  to  prove  a  source  of  trouble  than  a  cut  which 
bleeds  freely.  The  bites  of  insects  are,  with  certain  dis- 
eases, the  way  in  which  the  organism  is  introduced  into 
the  body.  Wounds  may  be  on  the  exterior  of  the  body, 
or  on  the  interior  surface,  as  in  the  mouth,  stomach,  or 
intestines. 

The  alimentary  tract  is  the  portal  of  entrance  for  some 
disease  producing-bacteria,  especially  for  those  that  pro- 
duce those  diseases  known  as  intestinal  diseases,  as  hog 
cholera  and  chicken  cholera.  In  these  diseases  the  bac- 
teria grow  in  the  intestines.  In  other  diseases  the  causal 
organisms  are  able  to  pass  through  the  walls  of  the  in- 
testines and  thus  get  into  the  blood  and  lymph  to  be 
carried  to  various  parts  of  the  body. 

The  air  passages  and  lungs  form  a  third  portal  of  en- 
trance. The  bacteria  in  the  dust  of  the  air  lodge  in  the 
various  parts  of  the  air  passages  or  in  the  lungs.  Influ- 
enza, pneumonia,  and  tuberculosis  may  be  acquired  in 
this  way. 

Exits  of  bacteria  from  the  body.  The  bacteria  once 
in  the  body  grow  in  various  parts,  depending  on  the  na- 
ture of  the  disease.  In  most  diseases  they  pass,  in 
greater  or  less  numbers,  from  the  body  of  the  animal  be- 
fore death  occurs.  They  are  thrown  off  in  the  manure  in 
the  case  of  intestinal  diseases,  such  as  hog  cholera ;  in  the 
urine ;  in  the  sputum,  as  in  tuberculosis  and  pneumonia ; 
in  the  contents  of  boils  and  ulcers,  as  in  glanders  and  py- 
•ogenic  troubles;  in  the  milk  when  the  udder  is  diseased, 
as  in  garget  and  tuberculosis,  and  in  the  blood  drawn 
from  the  body  by  sucking  insects.  After  death  by  the 


Transmissible  Diseases.  95 

t 

•decomposition  of  the  carcass,  the  bacteria  are  set  free 
unless,  as  frequently  happens,  the  process  of  putrefaction 
destroys  them. 

Spread  of  pathogenic  bacteria.  The  bacteria  are 
spread  from  place  to  place  by  insects  which  have  bitten 
the  living  animal  or  have  fed  on  the  carcass ;  by  birds,  and 
by  carnivorous  animals,  as  dogs.  The  bacteria  may  be 
carried  long  distances  in  water,  or  by  wind  as  dust  in  the 
air ;  on  the  clothes  and  shoes  of  attendants ;  on  farm  im- 
plements as  hoes,  shovels,  etc. ;  and  by  the  shipment  of 
infected  objects  such  as  hides. 

The  most  important  manner  in  which  the  disease-pro- 
ducing bacteria  are  spread  is  through  the  transfer  of 
diseased  animals  from  place  to  place.  All  of  our  import- 
ant transmissible  diseases  have  been  imported  to  this 
country  in  the  bodies  of  animals.  Constant  watch  has 
to  be  maintained  to  prevent  the  introduction  into  this 
country  of  some  diseases  that  are  widespread  in  Europe, 
such  as  foot  and  mouth  disease  and  contagious  pleuro- 
pneumonia  of  cattle. 

Susceptibility  to  transmissible  diseases.  In  order 
that  transmissible  diseases  may  develop,  it  is  necessary  to 
have  the  causal  organism  enter  the  body  of  a  susceptible 
animal  host.  Not  all  animals  are  susceptible  to  any  dis- 
ease. When  an  animal  does  not  afford  a  suitable  medium 
for  the  growth  of  the  parasite,  it  is  said  to  be  immune. 
Such  an  immunity  is  ' '  natural. ' '  Again  immunity  may 
be  "artificial,"  i.  e.,  induced  by  a  natural  attack  of  the 
disease,  or  by  the  introduction  of  some  immunizing  sub- 
stance into  the  body,  as  in  the  employment  of  vaccines 
in  black  leg  and  anthrax.  Some  diseases  affect  but  a 
single  kind  of  animal,  as  typhoid  fever  in  man,  or  hog 
cholera  in  hogs.  Again  a  large  number  of  kinds  may  be 


96  Agricultural  Bacteriology. 

subject  to  the  disease,  as  with  tuberculosis  which  natur- 
ally occurs  in  man,  cattle,  hogs,  fowls,  and  many  other 
animals. 

Period  of  incubation  of  transmissible  diseases.  A 
period  always  elapses  between  the  time  of  the  entrance 
of  the  bacteria  into  the  body  and  the  first  signs  of  illness. 
This  is  called  the  " period  of  incubation"  of  the  disease. 
It  may  be  but  a  few  days  in  length,  as  in  the  case  of 
anthrax,  or  from  several  weeks  to  months,  as  with  tuber- 
culosis. 

Lesions  of  the  disease.  The  bacteria  produce  in  the 
body  of  the  affected  animal  more  or  less  characteristic 
symptoms  and  changes.  By  these  alone,  one  is  often 
able  to  determine  the  disease  present.  The  changes  in 
the  different  organs  of  the  body  from  their  normal  condi- 
tion, due  to  the  action  of  the  disease-producing  organ- 
ism, are  known  as  the  ' '  lesions. ' '  A  post-mortem  exami- 
nation of  any  animal  that  has  died  of  a  suspected  trans- 
missible disease  should  always  be  made  so  as  to  render- 
more  certain  a  correct  diagnosis.  Precautionary  meas- 
ures which  will  be  described  later  should,  however,  be 
taken  in  making  such  examinations,  in  order  to  prevent 
further  trouble. 

The  various  transmissible  diseases  differ  greatly  in  the 
rapidity  with  which  they  progress  in  the  animal.  An- 
thrax usually  kills  the  animal  in  a  few  days,  while  with 
tuberculosis  an  animal  may  live  for  years. 

Necessity  of  diagnosis  of  transmissible  disease.  With 
those  diseases  caused  by  some  form  of  bodily  disturbance, 
it  is  of  small  importance,  except  for  determining  the  kind 
of  treatment  to  apply,  whether  a  correct  diagnosis  of  the 
disease  is  made  or  not,  since  the  disease  can  not  spread  to 


Transmissible  Diseases.  97 

the  other  members  of  the  herd.  With  the  contagious 
diseases,  it  is  of  the  greatest  importance  that  an  early 
and  correct  diagnosis  of  the  trouble  be  made  so  that  pro- 
per means  may  be  taken  to  prevent  the  spread  of  the  dis- 
ease in  the  herd. 

In  the  following  pages  the  general  characteristics  of 
the  transmissible  diseases  most  likely  to  be  met  by  the 
stockman  in  his  herd  and  flocks  are  given.  The  farmer 
must  usually  rely  for  a  diagnosis  of  any  disease  on  the 
experienced  veterinarian  who  must  often  call  to  his  aid 
the  facilities  of  a  bacteriological  laboratory. 

Treatment  and  prevention  of  transmissible  diseases. 
With  most  of  the  transmissible  diseases  but  little  can  be 
done  so  far  as  treatment  of  the  infected  animal  is  con- 
cerned. Especially  is  this  true  when  the  period  of  incu- 
bation of  the  disease  is  past  and  the  causal  organism  is 
established  in  the  body  of  the  animal.  The  disease  must 
be  allowed  to  run  its  course  in  the  individual  animal. 
Much  can  be  done  in  preventing  the  disease,  either  in 
keeping  it  out  of  the  herds  and  flocks,  or  in  limiting  its 
spread  when  once  introduced.  The  transmissible  diseases 
are  often  called  preventable  diseases.  The  prevention  is 
accomplished  by  not  allowing  contact  of  the  animals  with 
any  materials  containing  the  causal  organism.  In  order 
to  do  this  in  an  intelligent  manner,  it  must  be  known  with 
certainty  which  disease  is  present ;  the  nature  of  the  or- 
ganism; its  manner  of  entering,  and  leaving  the  animal 
body,  etc. 

The  farmer  should  have  a  sufficient  knowledge  of  the 
nature  of  the  various  diseases  so  that  he  may  know  the 
proper  steps  to  take,  in  order  to  protect  his  animals  in 
outbreaks  of  the  different  transmissible  diseases. 


CHAPTER  X. 

ANTHRAX,  BLACK  LEG,  HEMORRHAGIC  SEPTI- 
CEMIA  AND  CORN  STALK  DISEASE. 

The  disease  of  anthrax  is  much  more  important  in 
Europe  than  in  this  country.  It  is,  however,  quite  com- 
mon in  Mississippi,  Louisiana,  and  Delaware  and  in 
many  other  states,  it  occurs  at  irregular  intervals.  It  is 
a  matter  of  much  importance  to  have  the  disease  break 
out  in  a  district  or  on  a  farm,  since  it  is  very  difficult  to 
rid  an  infected  area  of  the  disease,  if  it  once  becomes 
established. 

The  disease  is  one  which  affects  primarily  sheep,  cattle, 
and  horses,  although  other  domestic  animals  as  hogs, 
dogs,  and  cats  may  acquire  it.  Human  beings  may  be 
affected  with  it.  The  relation  of  bacteria  to  disease  was 
first  proven  in  the  case  of  anthrax.  The  organism  can 
be  easily  grown  in  the  laboratory  on  a  large  number  of 
substances.  While  the  anthrax  bacillus  can  grow  in  the 
animal  body  in  the  absence  of  free  oxygen,  it  can  not 
form  spores  except  in  contact  with  the  oxygen  of  the  air. 

Channels  of  infection.  The  bacteria  enter  the  body- 
in  a  number  of  ways.  If  the  food  or  water  is  contam- 
inated, they  enter  through  the  intestinal  wall.  The  dis- 
ease may  be  acquired  from  infected  hay  or  on  the  pas- 
ture. The  organisms  may  enter  the  body  by  way  of  the 
lungs,  in  the  dust  of  the  air,  or  may  be  introduced 
through  wounds,  especially  by  the  bites  of  flies  that  have 
had  access  to  the  carcass  or  body  of  an  affected  animal. 


Anthrax.  99 

It  is  thought  that  the  horse  fly  is  one  of  the  chief  means 
by  which  the  disease  is  spread  among  the  plantation 
mules  of  the  southern  states. 

Symptoms.  The  disease  appears  in  two  types,  in  one 
of  which  there  are  no  external  signs  of  trouble,  in  the 
other  swellings  or  carbuncles  develop  on  the  surface  of 
the  body.  The  type  showing  no  localization  on  the  sur- 
face of  the  body  is  most  common  in  cattle  and  sheep,  and 
is  due  to  infection  by  way  of  the  intestines.  "When  the 
organisms  have  been  introduced  through  a  wound,  they 
may  develop  at  the  point  of  introduction,  forming  a 
tumor  which  is  at  first  hard,  hot,  and  painful.  It  rapidly 
increases  in  size  and  becomes  cold  and  painless  due  to  the 
death  of  the  tissues.  If  the  tumor  is  opened  a  dark  tar- 
like  exudate  is  noted.  The  tumors  may  develop  in  the 
throat,  especially  in  hogs  and  dogs.  Gangrene  often  ap- 
pears in  the  tumor,  due  to  secondary  infection  with  pu- 
trefactive bacteria. 

The  disease  varies  widely  in  its  duration.  The  first 
animals  to  die  in  an  outbreak  may  show  no  symptoms 
whatever,  but  may  be  found  dead  in  the  pasture.  Others 
may  show  signs  of  illness  for  a  few  hours,  and  the  last 
animals  to  die  may  have  had  the  disease  for  several  days. 
In  the  less  rapid  forms  of  the  disease,  the  temperature 
rises  to  105°-108°  F.  The  animal  may  be  restless, 
stamping  the  ground,  running  about,  and  at  last  going 
into  convulsions,  which  are  followed  by  death.  If  the 
lungs  are  affected,  the  animal  has  difficulty  in  breathing. 
In  case  the  carbuncles  are  noted,  the  duration  of  the 
disease  is  likely  to  be  longer  than  when  the  infection  is 
more  general. 

Post-mortem  examination.  The  most  prominent 
changes  to  be  noted  on  post-mortem  examination  are  the 


100  Agricultural  Bacteriology. 

enlarged  spleen  (milt)  which  is  often  several  times  its 
normal  size,  and  much  darker  in  color  than  normally.  It 
is  soft  and  friable.  The  blood  is  not  bright  red,  but  is 
of  a  dark,  tarry  appearance,  and  does  not  coagulate  as 
does  normal  blood.  Shortly  before  death,  a  dark  bloody 
exudate  may  be  noted  coming  from  the  natural  openings 
of  the  body,  nose,  mouth,  and  anus.  The  urine  may  also 
be  dark  in  color.  The  intestines  may  be  affected,  in 
which  case  the  contents  are  bloody.  The  carcass  begins 
to  putrefy  very  soon  and  the  stiffness  of  the  body  noted 
after  death  from  other  causes  is  absent. 

Differential  diagnosis.  It  is  very  important  to  dif- 
ferentiate this  disease  from  others,  such  as  black  leg  and 
hemorrhagic  septicaemia,  which  are  often  mistaken  for 
anthrax.  The  precautions  that  must  be  taken  to  prevent 
further  spread  in  the  herd  differ  from  those  to  be  em- 
ployed with  these  diseases.  On  account  of  the  sudden- 
ness of  the  death  of  the  first  animals  affected,  the  farmer 
is  likely  to  think  they  were  poisoned  or  were  killed  by 
lightning.  The  changes  peculiar  to  the  disease  may  be 
absent,  in  which  case  a  bacteriological  examination  is 
necessary  in  order  to  establish  the  nature  of  the  disease. 

General  precautions.  The  bacteria  found  in  immense 
numbers  in  the  blood,  form  spores  as  soon  as  the  blood  is 
allowed  to  escape  from  the  body,  as  happens  in  making  a 
post-mortem  examination.  If  the  body  is  unopened 
spores  can  not  form.  As  previously  noted  there  is  often 
a  discharge  from  the  natural  openings  of  the  body.  This 
will  contain  the  organisms.  The  spot  where  the  animal 
dies  is  thus  certain  to  be  infected.  The  spores  will  re- 
main in  the  soil  of  pastures  and  fields  for  years,  and  such 
a  contaminated  pasture  can  not  be  used  with  safety. 

In  order  to  prevent  the  general  spread  of  the  disease, 


Anthrax.  101 

and  the  infection  of  pastures,  as  well  as  to  prevent  the 
danger  of  accidental  infection  the  greatest  precautions 
should  be  taken  in  the  handling  of  anthrax  carcasses. 
The  carcass  should  not  be  skinned,  or  dragged  on  the 
ground  to  place  of  burial,  as  this  treatment  will  give  op- 
portunity for  dispersal  of  spores. 

If  there  is  any  reason  to  suspect  that  an  animal  has 
died  of  anthrax,  an  examination  should  be  made,  by  a 
veterinarian  if  possible.  A  small  portion  of  the  spleen 
or  preferably  an  ear  should  be  sent  to  some  laboratory* 
for  diagnosis  in  case  the  decision  can  not  be  made  on  the 
results  of  the  post-mortem  examination  alone.  Tissues 
of  all  kinds  that  are  to  be  sent  to  a  laboratory  for  exami- 
nation should  be  placed  in  a  clean  vessel  that  can  be 
sealed  tightly  such  as  a  fruit  j'ar.  This  should  be  packed 
in  sawdust  or  shavings  and  ice  so  that  it  may  reach  the 
laboratory  in  such  a  condition  that  an  examination  can 
be  made. 

After  examination  the  carcass  should,  if  possible,  be 
burned.  If  this  is  not  possible,  it  should  be  buried 
deeply,  covering  well  with  lime  before  replacing  the  dirt. 
The  place  of  burial  should  be  protected  by  fencing  off 
the  same  if  it  happens  to  be  in  the  pjasture.  If  the 
disease  of  anthrax  breaks  out  while  the  cattle  are  on  the 
pasture,  all  those  that  show  no  signs  of  illness  should  be 
at  once  removed  and  vaccinated.  The  temperatures  of 
the  healthy  animals  should  be  taken  morning  and  even- 
ing for  two  weeks,  and  any  animals  showing  an  abnor- 
mally high  temperature,  105°  F.  or  higher,  should  be  re- 
moved at  once  from^the  herd. 


*  Many  states  maintain  laboratories  under  the  direction  of 
the  Live  Stock  Sanitary  Boards  or  Experiment  Stations  for  the 
examination  of  such  material. 


102  Agricultural  Bacteriology. 

Vaccination  against  anthrax.  There  are  a  number 
of  infectious  diseases  which  affect,  as  a  rule,  the  individ- 
ual but  once.  Measles,  mumps,  and  small  pox  are  ex- 
amples of  such  diseases  in  man.  The  first  attack  pro- 
tects the  individual  against  a  subsequent  one.  The  exact 
reason  for  this  protection,  which  may  last  during  the 
life  of  the  individual  or  for  a  shorter  time,  is  not  fully 
known.  This  immunity  is  called  " acquired"  as  opposed 
to  "natural"  immunity.  Jenner  was  the  first  to  show 
in  the  case  of  small  pox  that  protection  might  be  pro- 
duced by  artificially  inoculating  the  individual  with  a 
weakened  virus,  that  this  inoculation  was  without  danger 
to  the  individual,  and  yet  protected  him  from  acquiring 
the  virulent  disease.  The  small  pox  virus  is  weakened 
by  passing  it  through  the  body  of  a  calf  so  that  it  is  no 
longer  able  to  produce  a  general  infection  but  only  a  sore 
at  the  point  of  inoculation.  Later  Pasteur  discovered 
that  certain  other  diseases  caused  by  bacteria  could  be 
prevented  by  vaccination.  In  all  cases  the  vaccine  is 
prepared  by  the  use  of  the  specific  organism  of  the  dis- 
ease in  question  that  has  been  artificially  weakened  or 
reduced  in  virulence  in  a  variety  of  ways.  These  meth- 
ods will  be  given  under  the  various  diseases  for  which 
vaccines  are  employed. 

In  the  case  of  anthrax  the  vaccine  is  prepared  by  grow- 
ing the  anthrax  bacillus  at  a  high  temperature  for  several 
days.  This  decreases  its  virulence.  It  is  desirable  to 
have  a  vaccine  of  a  virulence  sufficient  to  produce  a  mild 
fever  in  the  animal,  or  there  will  be  no  immunity  pro- 
duced. 

The  vaccine,  as  used  is  prepared  in  a  variety  of  ways. 
It  should  be  applied  only  by  an  experienced  veterinarian. 
Care  must  be  exercised  in  its  use,  because  in  it  are  living 


Anthrax.  103 

organisms,  which,  under  some  conditions  it  is  claimed 
may  regain  their  virulence.  The  protection  afforded  by 
the  vaccination  lasts  less  than  a  year,  hence  if  cattle  are 
to  be  turned  onto  infected  pastures,  the  process  of  vacci- 
nation must  be  repeated  yearly. 

The  disease  is  often  spread  from  one  place  to  another 
by  means  of  infected  hides,  wool,  and  bristles.  Hides 
imported  into  this  country  have  been  shown  to  be  the 
cause  of  a  number  of  outbreaks.  The  disease  is  spread 
from  tannery  refuse  which  is  usually  turned  into  flowing 
streams.  Animals  may  become  infected  by  drinking  the 
water  or  by  grazing  on  lands  subject  to  overflow.  Epi- 
demics of  anthrax  have  been  caused  in  this  manner  in 
Wisconsin,  Pennsylvania,  and  Delaware. 

The  disease  occurs  in  human  beings,  especially  in  the 
case  of  tannery  operators  and  workers  in  woolen  mills 
and  brush  factories.  The  spores  are  breathed  in  or  are 
introduced  into  wounds.  Anthrax  is  often  called  ' '  wool 
sorters"  disease  in  human  beings.  If  the  infection  is 
through  a  wound,  a  carbuncle  usually  results,  if  the  in- 
fection is  by  way  of  the  lungs  the  disease  is  often  of  a 
generalized  and  fatal  type. 

The  farmer  who  suspects  anthrax  amongst  his  animals 
can  not  be  too  careful.  The  dead  animal  should  be  ex- 
amined but  should  be  opened  only  at  the  place  where  the 
carcass  is  to  be  disposed  of  so  as  to  prevent  the  infection 
of  yards,  barns  and  fields.  The  person  making  the  ex- 
amination should  see  that  his  hands  are  free  from  ab- 
rasions or  cuts.  It  is  helpful  to  have  the  hands  coated 
with  lard  or  vaseline.  Care  should  be  taken  to  prevent 
the  contamination  of  shoes  and  clothing.  The  utensils 
used  in  the  examination  should  be  disinfected  at  once, 
preferably  by  heating  them  in  a  fire,  or  by  boiling  in 


104  Agricultural  Bacteriology. 

water  for  an  hour.  The  carcass  should  be  disposed  of  at 
once  after  opening  so  that  flies  shall  not  have  access  to 
the  blood. 

It  should  also  be  remembered  that  the  urine,  f  eces,  and 
discharges  from  the  nostrils  may  contain  the  organisms. 
Barns  may  thus  become  contaminated,  and  where  spores 
form,  infection  persists  for  long  periods.  The  milk  may 
sometimes  contain  the  organisms  just  prior  to  the  death 
of  the  animal. 

BLACK  LEG. 

Black  leg  or  symptomatic  anthrax,  as  it  is  often  called, 
because  some  of  the  symptoms  and  lesions  resemble  those 
of  anthrax  is  a  disease  of  importance,  especially  in  the 
western  states  where  cattle  are  given  a  wide  range. 
While  found  in  the  majority  of  the  states,  in  other  than 
the  range  states  it  occurs  only  in  isolated  localities. 

Animals  affected.  The  animals  affected  are  cattle, 
sheep,  and  goats,  the  latter  two  very  infrequently.  No 
other  domestic  animal  is  susceptible  to  the  disease  nor  is 
man.  It  is  primarily  a  disease  of  young  cattle,  between 
the  age  of  six  months  and  two  years,  and  is  most  often 
noted  among  the  best  nourished  animals  of  the  hprd. 
Purebred  and  grade  animals  are  more  susceptible  than 
common  stock  of  the  range.  The  "long  horn"  of  the 
Texas  ranges  did  not  easily  acquire  black  leg  but  with 
the  introduction  of  purebred  stock  the  disease  has  in- 
creased greatly  in  amount.  In  the  northern  states  it  is 
most  frequent  from  April  to  September,  in  the  south  it 
occurs  at  all  times  of  the  year. 

Symptoms.  The  organism  is  supposed  to  enter  the 
body  through  wounds  on  the  skin  or  mucous  membranes 
of  the  mouth  and  intestines.  So  far  as  is  known  the  bac- 


Black  Leg  105 

teria  do  not  enter  the  body  in  the  feed  or  air.  The 
period  of  incubation  of  the  disease  is  not  known,  but  it  is 
supposed  to  be  very  short.  The  symptoms  resemble 
quite  closely  those  of  anthrax.  The  animal  has  a  fever 
and  suffers  loss  of  appetite  and  rumination.  Tumors  or 
carbuncles  may  appear  on  the  surface  of  the  body,  es- 
pecially on  the  thighs  and  shoulders,  but  not  below  the 
knee  or  hock  joints  or  on  the  tail.  The  swelling  is  at  first 
small  and  painful.  Later  it  increases  in  size,  and  be- 
comes cold  and  painless,  owing  to  the  death  of  the  tis- 
sue. When  the  hand  is  passed  over  the  swelling,  gas  can 
be  noted  in  the  tissue,  making  a  crackling  sound  under 
pressure.  When  opened  a  dark  frothy  liquid  exudes 
which  has  a  disagreeable  odor.  The  disease  is  usually 
fatal.  The  period  of  illness  one  to  three  days. 

Post-mortem  examination.  In  a  post-mortem  exam- 
ination the  muscles  about  the  tumors  appear  dark  in 
color,  hence  the  name  "black  leg."  The  muscle  fibres 
of  the  tissue  affected  by  the  carbuncle  are  forced  apart 
by  the  gas.  The  production  of  gas  in  the  body  continues 
after  death,  producing  a  bloated  condition  of  the  car- 
cass. The  tumors  are  much  like  those  found  in  anthrax, 
except  that  in  anthrax  tumors  no  gas  is  present. 

The  blood  in  black  leg  is  normal  in  color  and  in  coagu- 
lating properties,  the  spleen  is  not  enlarged.  These 
often  enable  it  to  be  distinguished  from  anthrax. 

General  precautions.  The  organism  causing  black 
leg  is  an  anaerobic  one.  It  produces  spores  in  the  car- 
cass of  the  dead  animal,  even  when  unopened,  as  oxygen 
is  not  necessary  for  spore  formation.  If  the  body  is 
opened  and  the  soil  polluted  by  blood,  the  organisms  will 
persist  for  a  long  time  in  the  field.  The  same  care 
should  be  taken  as  in  anthrax  in  making  a  post-mortem 


106  Agricultural  Bacteriology. 

examination,  to  prevent  soil  contamination.  There  is 
not  the  same  danger,  however,  to  the  person  making  the 
examination  as  the  disease  does  not  affect  man.  The  dis- 
posal of  the  carcass  should  be  done  either  by  burning  or 
burying  it  deeply  in  a  place  where  it  can  not  be  washed 
out  or  dogs  dig  it  out.  The  skin  should  not  be  removed. 
The  place  where  the  animal  lay  at  the  time  of  death 
should  be  disinfected. 

If  the  disease  breaks  out  in  a  herd,  the  animals  that 
show  no  signs  of  illness  should  be  at  once  removed  from 
the  pasture  while  the  sick  ones  are  confined  to  a  small 
range.  The  healthy  animals  should  be  vaccinated. 
Here  as  in  anthrax  the  vaccine  contains  the  disease-pro- 
ducing bacteria  in  a  weakened  form.  The  vaccine  is 
made  by  taking  the  meat  from  a  fresh  black-leg  tumor, 
pounding  it  in  a  mortar  with  a  little  water,  and  squeezing 
the  pulp  through  a  cloth.  This  filtrate  is  allowed  to  dry. 
It  can  be  kept  in  this  dry  form  for  a  long  time.  The 
organism  is  weakened  by  heating  this  powder  to  about 
210°  F.  for  6  hours.  It  is  prepared  for  injection  into 
the  animal  by  suspending  the  powder  in  water.  A 
definite  mixture  is  made,  one  cubic  centimeter  of  which 
is  injected  beneath  the  skin  of  the  animal.  Some  of  the 
commercial  firms  put  up  the  vaccine  in  the  form  of  a 
small  pellet  which  can  be  introduced  readily  beneath  the 
skin  of  the  animal  by  means  of  a  special  syringe.  An- 
other form  consists  of  a  bunch  of  threads  which  are  in- 
serted beneath  the  skin  by  a  special  instrument.  The 
vaccine  is  used  especially  on  the  ranges,  where  large  num- 
bers of  animals  must  be  vaccinated,  and  it  is  desirable  to 
have  the  vaccine  in  as  convenient  form  as  possible. 

The  Bureau  of  Animal  Industry  of  the  U.  S.  Depart- 
ment of  Agriculture  sends  the  vaccine  to  the  farmers 


Hemorrhagic  Septicemia.  10T 

whose  herds  are  affected.  In  1907,  1,200,000  doses  were 
sent  out.  Its  use  has  been  very  successful.  On  the 
large  ranges  before  vaccination  was  carried  out  the  loss 
amounted  to  about  10  per  cent,  of  the  annual  calf  crop. 
By  vaccination  the  loss  has  been  reduced  to  less  than 
0.5  per  cent. 

HEMORRHAGIC  SEPTICEMIA. 

By  ' '  septicemia ' '  is  meant  a  disease  in  which  the  bac- 
teria are  found  especially  in  the  blood.  The  phrase 
1 1 blood  poisoning"  is  also  used  to  refer  to  such  diseases. 
Anthrax  may  be  called  a  septicemic  disease  for  the  organ- 
isms are  found  in  every  drop  of  blood.  Hemorrhagic 
septicemia  is  a  type  of  blood-poisoning  which  is  charac- 
terized by  hemorrhages  in  various  parts  of  the  body. . 
By  a  hemorrhage  is  meant  the  passage  of  the  blood  out  of 
the  blood  vessels  into  the  tissue. 

This  disease  is  found  in  all  parts  of  the  world.  In  our 
own  country  it  occurs  most  frequently  in  the  upper  Mis- 
sissippi valley.  In  Europe  it  has  caused  great  losses, 
among  the  wild  animals,  deer  and  wild-boar. 

The  way  in  Avhich  it  is  introduced  into  a  herd  is  un- 
known, as  well  as  its  passage  from  one  animal  to  another. 
The  normal  habitat  of  the  bacteria  is  also  unknown.  The 
disease  is  likely  to  appear  suddenly  in  a  herd,  destroy  a 
large  part  of  the  same  and  disappear  as  mysteriously  as 
it  came. 

The  rapidity  of  its  appearance  and  the  suddenness 
with  which  the  animals  die,  together  with  the  helpless- 
ness of  the  owner  to  contend  with  it,  make  it  a  disease 
much  to  be  dreaded.  Frequently  the  animals  die  with- 
out any  previous  symptoms  of  illness.  This  may  lead 
the  owner  to  think  the  animals  have  been  poisoned. 


308  Agricultural  Bacteriology. 

<Dows  which  gave  the  usual  amount  of  milk  in  the  morn- 
ing, may  give  none  at  night,  and  be  found  dead  by  the 
next  morning.  The  symptoms  are  often  quite  similar  to 
those  of  milk  fever.  The  animal  is  weak,  staggers  in 
walking,  and  the  extremities  are  cold.  The  duration  of 
the  disease  is,  as  indicated,  short.  Recovery  is  rare. 

Post-mortem  examination.  On  post-mortem  exami- 
nation red  spots  from  the  size  of  the  head  of  a  pin  to  sev- 
eral inches  in  diameter  are  found  beneath  the  skin. 
Hemorrhagic  areas  are  also  found  on  the  heart,  stomach, 
and  intestines.  The  blood  is  red  and  coagulates  in  a 
normal  manner.  The  spleen  is  also  normal.  The  disease 
is  often  confused  with  anthrax  on  account  of  the  sudden 
death  of  the  animals.  It  is,  however,  very  important 
that  a  correct  diagnosis  be  made,  for  the  methods  of 
treatment  and  prevention  are  different.  The  enlarged 
spleen  and  the  dark  colored  blood  in  anthrax  serve,  us- 
ually, to  differentiate  that  disease  from  hemorrhagic  sep- 
ticemia,  while  such  tumors  as  are  found  in  black  leg  do 
not  occur  in  this  disease.  Some  times  it  is  difficult  to 
tell  which  disease  is  present  from  an  examination  of  the 
carcass.  Recourse  must  then  be  had  to  bacteriological 
examination  of  the  blood,  a  sample  of  which  should  be 
sent  to  the  state  authorities  having  charge  of  the  live 
stock  interests.  No  treatment  is  of  any  value,  no  vaccine 
can  be  used  nor  an  antitoxin  as  in  the  case  of  tetanus. 

In  order  to  prevent  the  spread  of  the  disease,  in  the 
herd,  it  is  necessary  to  isolate  each  animal  from  every 
other  animal  of  the  herd.  This  can  be  done  by  staking 
the  animals  out.  They  should  be  removed  from  the  in- 
fected pasture  to  a  fresh  one  or  to  a  meadow  and  tied 
with  ropes. 

The  carcasses  should  be  burned  or  buried  deeply  and 


Corn  Stalk  Disease.  109- 

every  precaution  should  be  taken  to  prevent  the  spread 
of  the  disease.  If  animals  die  in  the  barn,  the  litter 
should  be  burned  and  the  stable  cleaned  and  disinfected. 
The  organism  does  not  form  spores,  hence  is  easily  de- 
stroyed in  stables  through  the  use  of  disinfectants. 

CORN  STALK  DISEASE. 

In  those  sections  of  the  country  in  which  it  is  the  cus- 
tom to  pick  the  corn  from  the  standing  stalks,  and  then 
turn  cattle  into  the  fields,  a  disease  known  as  ' '  corn  stalk 
disease ' '  is  sometimes  encountered.  The  trouble  appears 
soon  after  the  cattle  are  turned  into  the  corn  field  (4  to 
10  days).  It  appears  without  warning  and  kills  the  cat- 
tle very  quickly.  Animals  that  seem  to  be  well  at  night 
are  found  dead  in  the  morning.  Usually  all  of  the  ani- 
mals that  die  of  this  trouble  are  lost  in  a  single  day  or  at 
least  in  a  few  days. 

On  account  of  the  suddenness  with  which  death  occurs, 
and  the  large  losses  which  follow  in  a  short  time,  it  is 
often  taken  for  a  specific  contagious  disease,  especially 
for  anthrax,  black  leg,  or  hemorrhagic  septicaemia.  It 
is  important  to  differentiate  the  disease  from  those  men- 
tioned. This  can  be  done  by  the  relation  of  the  appear- 
ance of  the  disease  in  the  herd  to  the  period  of  allowing 
the  cattle  access  to  the  stalks,  and  by  the  fact  that  in 
corn-stalk  disease  the  tissues  appear  normal  on  post-mor- 
tem examination. 


CHAPTER  XI. 
TUBERCULOSIS. 

This  disease  is  known  by  many  names,  consumption, 
-or  phthisis  in  man,  grapes  or  pearl  disease  in  cattle ;  it  is 
also  often  called  the  great  "white  plague."  It  is  charac- 
terised by  the  formation  in  the  body  of  nodules  or  tu- 
bercles, hence  the  name  tuberculosis.  It  is  the  most  im- 
portant disease  of  man,  as  well  of  domestic  animals.  It 
causes  one  seventh  of  all  deaths  of  human  beings,  and  a 
much  larger  proportion  of  the  deaths  of  people  between 
the  ages  of  twenty  and  forty  years. 

Animals  affected.  All  of  the  domestic  animals  may 
be  affected,  but  it  is  most  prevalent  amongst  cattle,  hogs, 
and  hens;  much  less  so  amongst  horses,  sheep,  dogs  and 
-cats.  From  an  economic  or  a  hygienic  standpoint,  con- 
sideration need  be  given  to  the  disease  only  as  it  appears 
in  cattle,  hogs,  and  fowls. 

Geographical  distribution  of  tuberculosis.  The  dis- 
ease is  world- wide  in  the  case  of  man  and  almost  equally 
so  in  cattle.  All  the  important  special  breeds  of  cattle 
have  originated  in  Northwestern  Europe ;  from  here  they 
have  been  carried  to  all  parts  of  the  world,  and  they  have 
carried  with  them  this  disease.  The-  native  cattle  of  most 
countries  were  free  from  tuberculosis  until  the  improved 
breeds  were  introduced.  The  islands  of  Jersey  and 
Guernsey  are  free  from  bovine  tuberculosis,  and  are  kept 
free  because  no  live  cattle  are  imported. 


Tuberculosis.  Ill 

In  the  European  countries,  where  dairying  has  long 
l>een  carried  on,  the  disease  is  very  widespread.  In  soma 
of  the  German  states  30  per  cent  of  the  cattle  are  dis- 
eased ;  in  Belgium  48  per  cent ;  in  Denmark  after  fifteen 
years  of  warfare  against  it,  the  percentage  of  dairy 
cows  affected  has  been  reduced  from  40  to  10  per  cent; 
in  England  35  per  cent  of  the  cattle  are  affected.  In 
some  of  our  eastern  states,  as  Massachusetts,  26  per  cent 
of  the  dairy  cows  have  the  disease.  The  amount  of  the 
disease  is  less  in  the  western  states,  probably  from  5  to 
10  per  cent  of  the  milch  cows  of  Wisconsin,  Minnesota, 
Iowa  anji  Illinois  are  affected. 

It  is  not  evenly  distributed,  but  is  most  prevalent  in 
those  districts  where  improved  dairying  has  been  longest 
carried  on,  and  where  buying  and  selling  of  milch  cows 
is  general,  as  in  the  districts  furnishing  milk  to  the  cities. 
It  is  more  often  found  in  pure-bred  herds  than  in  those 
of  common  stock,  not  because  pure-bred  cattle  are  more 
susceptible,  but  because  more  animals  are  bought  into 
and  sold  from  such  herds.  There  is  little  or  no  differ- 
ence in  the  susceptibility  of  the  various  breeds;  Jerseys 
are  free  from  it  on  the  island  of  Jersey,  but  acquire  it, 
when  brought  in  contact  with  diseased  cattle.  The  beef- 
breeds  are  as  easily  infected  as  any  of  the  dairy  breeds. 
It  is  more  often  present  in  large  herds  than  in  small 
ones,  as  each  animal  purchased  may  be  the  means  of  in- 
troducing the  disease  into  the  herd. 

Distribution  and  appearance  of  diseased  tissues. 
The  disease  is  commonly  associated  with  an  affection  of 
the  lungs  and  indeed  this  organ  is  most  often  attacked. 
Every  part  of  the  body,  however,  may  be  diseased — heart, 
liver,  spleen,  muscles,  brain,  and  skin  may  be  affected. 
The  lymph  glands  that  are  found  in  the  neck,  along 


112  Agricultural  Bacteriology. 

the  windpipe,  and  close  to  the  intestine  are  usually  the- 
first  to  be  affected.  In  making  a  post-mortem  examina- 
tion of  the  suspected  animal,  the  parts  that  should  be 
examined  are  the  lungs,  the  lymph  glands  mentioned 
above,  liver  and  the  spleen. 

The  tubercles  vary  greatly  in  size,  from  a  pinhead  to 
the  size  of  a  hazelnut  or  walnut.  When  opened,  the 
smaller  tubercles  are  usually  of  a  light  gray  color 
throughout,  or  may  show  at  the  center  a  yellowish  spot. 
The  larger  tubercles  will  usually  contain  yellowish: 


FIG.  12.— TUBERCULOUS  OMENTUM. 

The  omentum,  a"  membrane  of  the  abdominal  cavity, 
is  normally  smooth  and  thin.  It  is  here  studded 
with  masses  of  small  tubercles.  From  a  gener- 
alized case  of  bovine  tuberculosis. 

material  and  in  many  of  the  organs,  as  in  the  liverr 
spleen,  and  lungs,  tubercular  abscesses  of  varying  size- 
may  be  formed.  Some  of  the  lymph  glands  become 
very  greatly  enlarged.  They  may  be  filled  with  creamy 
pus,  or  with  a  hard,  gritty,  yellowish  substance,  which 
is  produced  by  the  accumulation  of  lime  salts.  On  ac- 
count of  the  yellow  granular  appearance,  the  contents 


Tuberculosis.  113 

are  often  said  to  look  like  corn  meal.  The  healthy 
lymph  glands  are  of  uniform  color  throughout,  or  in  the 
older  animals  they  may  be  filled  with  a  black  pigment. 
The  tuberculous  gland  will,  on  section,  show  a  larger  or 
smaller  diseased  area,  apparent  by  its  yellow  color. 

The  lungs  of  a  healthy  animal  are  light  pink  in  color 
and  spongy  in  texture;  when  tuberculous,  the  tissue  is 
consolidated,  abscesses  or  affected  areas  appearing  in  the 
lung  tissue  or  even  raised  from  the  surface.  The  bron- 
chial glands  located  at  the  fork  of  the  windpipe  and 
imbedded  in  the  lung  tissue  are  often  early  affected. 
The  diseased  organs  are  usually  much  enlarged  and 
owing  to  the  consolidation  of  tissue  may  be  very  heavy. 

The  udder  is  sometimes  affected.  The  normal  udder 
should  be  uniformly  soft;  the  tuberculous  udder  often 
contains  hard  bunches  or  nodules.  As  the  disease 
progresses  an  entire  quarter  may  become  enlarged,  and 
very  hard.  There  is  no  fever  or  painful  swelling  as  in 
garget.  Tuberculosis  of  the  udder  is  important  because 
the  milk  is  then  certain  to  contain  the  tubercle  or- 
ganisms. 

The  bacteria  are  discharged  from  the  body  of  an 
animal  in  a  number  of  ways.  The  tubercles  in  the  lungs 
may  discharge  their  contents  into  the  air  passages;  the 
material  is  coughed  up,  a  portion  ejected  from  the 
mouth  during  the  act  of  coughing,  the  major -part  being 
swallowed.  The  sputum  is  digested,  the  tubercle 
bacilli  set  free,  and  they  pass  unharmed  through  the 
stomach  and  intestines  and  are  voided  with  the  manure. 
When  the  intestines  are  involved,  the  organisms  also 
appear  in  the  manure.  From  diseased  kidneys  or  blad- 
der, they  pass  off  in  the  urine,  and  from  the  udder,  in 
the  milk.  Animals  shedding  organisms  in  this  way  are 


Agricultural  Bacteriology. 

said  to  have  "open"  tuberculosis,  and  are  a  special 
menace  to  the  remainder  of  the  herd.  "When  the  dis- 
ease is  confined  to  parts  of  the  body  that  have  no  exter- 
nal opening,  as  lymph  glands,  the  cow  is  said  to  have 
41  closed"  tuberculosis.  As  long  as  the  disease  remains 
"closed,"  the  animal  is  not  a  source  of  danger.  It  is 
impossible  to  foretell  when  the  "closed"  type  will 
change  to  the  "open,"  as  it  is  certain  to  do  sooner  or 
later  with  the  continued  development  of  the  disease. 
Hence  every  affected  animal  must  be  considered  a  menace, 
present  or  potential,  to  the  herd  and  to  the  public  health. 

Infection  of  the  animal.  The  bacteria  that  come 
from  diseased  animals  are  carried  into  healthy  animals 
in  the  dust  from  polluted  mangers  and  dried  manure. 
The  dust  may  enter  the  lungs  or  it  may  lodge  in  the 
throat.  The  food  may  be  soiled  by  the  sputum  of  an 
animal,  or  by  dust.  The  milk  fed  to  calves  and  hogs 
may  contain  the  bacteria,  which  then  pass  through  the 
walls  of  the  intestine  into  the  lymph  and  blood  streams 
and  are  carried  to  various  parts  of  the  body,  especially 
the  lungs  and  lymphatic  glands.  For  this  reason  these 
are  the  organs  most  often  affected.  Hogs  acquire  the 
disease  very  readily  when  fed  on  contaminated  milk, 
a  single  feeding  of  milk  containing  many  tubercle 
bacilli  suffices  to  infect  hogs.  Because  of  the  content  of 
manure  in  tubercle  organisms,  hogs  running  after  cattle 
in  the  feed-lot  are  as  likely  to  be  diseased  as  those  fed 
on  skim  milk.  » Animals  may  acquire  the  disease  by 
contact  with  a  diseased  animal,  as  for  instance  by  licking 
each  other.  Very  rarely  are  the  reproductive  organs 
affected,  and  the  calves  from  tuberculous  dams  are 
usually  healthy.  Because  of  this  fact,  it  is  possible  to 


Tuberculosis.  115 

raise  healthy  calves  from  diseased  mothers,  by  what  is 
known  as  the  Bang  system,  which  will  be  described  later. 

Infection  of  the  herd.  The  most  frequent  way  in 
which  the  disease  is  introduced  into  a  herd  is  by  the 
purchase  of  a  tuberculous  animal.  The  larger  the 
number  of  animals  purchased,  the  more  likely  is  the 
disease  to  be  introduced.  The  animal  purchased  may 
appear  healthy  and  may  not  at  the  moment  be  a  source 
of  danger,  but  is  certain  in  time  to  become  a  center 
from  which  the  disease  will  spread  throughout  the  herd. 
As  was  stated,  pure-bred  herds  are  often  diseased.  All 
too  often  has  a  man  introduced  the  disease  into  his  herd 
through  his  efforts  to  improve  his  stock  by  the  purchase 
of  a  pure-bred  sire. 

The  farmer  should  know  the  condition  of  every 
animal  he  buys.  He  will  use  great  precaution  to  avoid 
buying  an  unsound  horse,  but  the  purchase  of  such  an 
animal  is  not  to  be  compared  so  far  as  probable  future 
loss  is  concerned,  to  the  purchase  of  a  tuberculous  cow, 
for  the  trouble  from  which  the  horse  suffers  is  not  likely 
to  spread,  while  tuberculosis  will  surely  infect  others. 

Buy  pure-bred  animals  from  honest  breeders  whose 
herds  are  "known  to  be  free  from  tuberculosis  and  from 
no  others,  even  though  they  will  guarantee  the  condition 
of  the  animals. 

The  feeding  of  creamery  skim  milk  and  of  whey  is 
another- potent  means  of  introducing  the  disease  into  the 
herd.  The  patron  of  a  creamery  or  cheese  factory 
carries  to  his  calves  and  hogs  a  mixture  of  the  milk  of 
all  the  other  patrons.  In  case  there  are  tuberculous  cows 
in  any  of  the  herds,  the  milk  may  contain  tubercle 
bacilli.  The  farmer  can  protect  his  herd  from  such  in- 
fection by  the  use  of  a  farm  separator,  or  by  heating 


116  Agricultural  Bacteriology. 

the  skim  milk  and  whey  to  160°  F.  before  using.  In 
Denmark  and  Germany  such  a  treatment  of  skim  milk 
and  whey  by  the  creameries  and  cheese  factories  is  made 
compulsory.  Some  of  the  States  have  similar  laws.  It 
is  a  process  to  which  no  one  should  object.  The  butter 
and  cheese  maker  will  find  himself  repaid  in  the  im- 
proved quality  of  the  milk  furnished  him,  since  the 
milk  cans  are  not  polluted  with  injurious  bacteria  from 
dirty  whey  tanks.  The  farmer  will  find  that  the  heated 
whey  and  milk  will  keep  longer,  hence  will  be  sweet 
when  fed. 

Spread  of  the  disease  in  the  herd.  Any  animal  with 
open  tuberculosis  is  giving  off  the  tubercle  bacilli,  thus 
exposing  the  remainder  of  the  herd  to  infection.  The 
disease  may  spread  slowly  at  first,  but  as>  one  animal 
after  another  becomes  a  new  center  from  which  the  or- 
ganisms are  furnished,  the  rate  of  spread  increases. 
The  rate  of  distribution  is  well  shown  in  the  following 
case:  Twelve  healthy  animals  were  placed  in  a  stable 
occupied  by  a  diseased  herd.  In  six  months  nine  had 
become  infected  and  the  disease  had  made  such  headway 
that  four  did  not  pass  inspection  when  slaughtered  and 
examined  by  the  Federal  meat  inspectors. 

The  conditions  obtaining  in  the  barn  with  reference 
to  light  and  ventilation  will  exert  a  great  influence  on 
the  rate  of  dissemination  in  the  herd.  If  the  air  is  poor 
and  the  animals  are  forced  to  breathe  it  more*  or  less 
continuously  during  the  winter,  their  ability  to  ward  off 
the  disease  is  reduced.  Plenty  of  pure  air  is  necessary 
for  cattle  as  for  man. 

The  most  important  phase  of  the  modern  methods  of 
curing  tuberculosis  in  human  beings  is  to  live  out  of 
doors,  to  sleep  out  of  doors,  summer  and  winter.  Light 


Tuberculosis.  117 

has  an  injurious  effect  on  bacteria,  destroying  them 
within  a  few  moments  when  they  are  directly  exposed 
to  it.  It  has  been  shown  by  direct  experiment  that  the 
disease  will  spread  more  rapidly  in  unsanitary  barns, 
than  in  those  which  are  well  lighted  and  ventilated.  The 
use  of  whitewash  twice  a  year  is  advisable  as  it  has  a 
disinfecting  action  and  makes  the  stable  lighter. 

Symptoms  of  the  disease.  In  the  early  stages  there 
are  no  definite  symptoms.  The  disease  starts  in  some 
part  of  the  body,  usually  in  the  lymph  glands,  and  may 
make  headway  very  slowly.  For  years  it  may  be  con- 
fined to  a  single  gland,  ,but  sooner  or  later  on  account 
of  some  condition  that  may  temporarily  impair  the  re- 
sistance of  the  animal,  such  as  calving,  the  disease 
develops  more  rapidly.  In  the  last  stages  the  animal 
becomes  emaciated,  the  hair  is  rough,  the  eyes  sunken, 
the  head  extended;  the  appetite  may  be  good,  but  the 
food  apparently  has  no  effect.  If  the  lungs  are  in- 
volved the  animal  may  cough,  especially  when  forced  to 
move  rapidly  after  resting.  If  there  are  hard  painless 
swellings  in  the  region  of  the  throat  or  shoulders,  the 
animal  may  be  suspected  of  tuberculosis.  If  there  are 
hard  nodules  in  the  udder;  if  one  or  more  quarters  are 
enlarged  and  hard,  but  painless  and  cold,  or  if  the 
lymph  glands  at  the  top  and  rear  of  the  hind  quarters 
of  the  udder  are  enlarged,  suspicion  may  be  aroused. 
It  is  absolutely  impossible  for  the  most  experienced 
veterinarian,  in  the  great  majority  of  cases,  to  tell  from 
a  physical  examination  alone,  whether  the  animal  has 
tuberculosis  or  not,  or  predict  the  stage  of  the  disease. 
An  animal  may  be  the  picture  of  health  and  be  as  great 
a  source  of  danger  as  one  in  the  last  stages. 


118 


Agricultural  Bacteriology. 


Tuberculin  test.  The  only  way  by  which  it  can  be 
determined  with  certainty  whether  an  animal  has  tuber- 
culosis or  not  is  by  the  use  of  the  tuberculin  test.  Tu- 
berculin is  prepared  in  bacteriological  laboratories  by 
growing  the  tubercle  organisms  in  beef  broth  containing 
glycerin.  The  organism  produces  a  substance  in  the 
broth,  which,  when  injected  beneath  the  skin,  has  a 
peculiar  effect  on  a  diseased  animal,  causing  a  fever  for 
a  few  hours;  while  in  the  healthy  animal  it  has  no 
appreciable  effect.  The  beef  broth  is  heated,  and  filtered 


FIG.  13. — A  TUBERCULOUS  ANIMAL. 
A  cow  that  has  had  the  disease  for  five  years. 

through  porcelain,  so  that  the  tuberculin  as  used  con- 
tains neither  living  or  dead  bacilli,  but  is  simply  an 
extract  of  their  cells.  It  cannot  produce  the  disease  in 
healthy  animals  nor  does  it  cause  the  disease  to  spread 
in  affected  animals. 

The  test  is  made  by  taking  a  series  of  temperature- 
readings  on  the  animal,  injecting  the  tuberculin  beneath 


Tuberculosis. 


the  skin,  and  beginning  ten  hours  later,  a  second  series 
of  temperature  readings  is  taken.  From  a  comparison 
of  the  temperatures  before  and  after  the  injection  of 
tuberculin,  the  condition  of  the  individual  animal  is 
determined. 

Details   of   making  the  tuberculin   test.     The  first 
series  of  temperatures  must  be  taken  in  order  to  deter- 


FIG.  14. — A  TUBERCULOUS  ANIMAL. 
An  advanced  case  of  generalized  tuberculosis.     Six 
weeks  before  the  photograph  was  taken  the  ani- 
mal was  in  as  fine  condition  as  the  one  shown  in 
Fig.   13. 

mine  the  normal  temperature  of  the  animal,  since  the 
temperature  of  the  cow  is  not  constant  like  that  of  man, 
but  varies  from  hour  to  hour  in  the  same  animal  and  in 
different  individuals.  The  average  temperature  of 
healthy  milch  cows  ranges  from  101°  to  102°  F.  The 
temperature  of  fat  stock  and  calves  is  higher ;  of  old  and) 


120 


Agricultural  Bacteriology. 


poor  cows  lower.  The  variation  in  the  normal  individual 
animal  may  range  from  99°  F.  to  103°  F.  The  varia- 
tion that  may  occur  in  the  temperature  of  a  well-kept 
healthy  animal  is  shown  in  the  following  table  in  which 
are  given  the  temperatures  of  two  healthy  cows  for 
twenty-four  hours,  together  with  the  rate  of  pulse  and 
the  number  of  respirations  per  minute.  Exercise,  ex- 
citement, and  hot  weather  increase  the  temperature.  A 
hot  spell  causes  a  rise  of  two  and  sometimes  four  degrees. 
The  drinking  of  cold  water  lowers  the  temperature. 

Temperature,  Rate  of  Pulse,  and  Respirations  per  Minute. 


Co\ 

r  No.  1 

Co 

iv  No.  2 

Tempera- 
ture 

Pulse 

Resp. 

Tempera- 
ture 

Pulse 

Resp. 

10  A    M             

99  5°F 

66 

18 

98.6°F 

60 

15 

12  A    M     

100  8 

54 

15 

99.4 

54 

15 

2PM            

101  6 

48 

15 

100.2 

54 

18 

4  P    M 

108 

66 

24 

102.7 

72 

24 

6  p    M             

103  1 

57 

18 

103. 

60 

27 

8  P    M 

103 

56 

16 

102. 

60 

24 

10P    M  

102. 

60 

20 

102. 

50 

18 

12  P    M 

102  5 

56 

'     16 

101  6 

54 

20 

2A    M... 

102.4 

64 

18 

102.2 

58 

18 

4AM 

102  2 

54 

24 

101.5 

60 

24 

6  A    M  

101.8 

60 

18 

102.2 

60 

20 

8  A.  M  

102.5 

56 

16 

103.2 

60 

18 

The  temperature  is  taken  in  the  rectum  by  means  of  a 
clinical  or  fever  thermometer,  similar  to  those  used  by 
physicians.  The  mercury  in  these  thermometers  cloes 
not  run  down,  but  stays  at  the  highest  point  reached, 
i.  e.,  registers,  until  shaken  down.  Veterinary  ther- 
mometers of  heavy  glass  with  a  ring  at  the  end  are  best ; 
a  string  is  attached  to  the  ring  and  to  a  small  paper 
clamp.  When  the  thermometer  is  inserted  in  the 
animal,  the  clamp  is  attached  to  the  long  hair  at  the 
base  of  the  tail.  In  this  way  the  thermometer,  if  ejected 
by  the  animal,  will  not  be  lost  or  broken  on  the  floor. 


Tuberculosis.  121 

The  mercury  should  always  be  shaken  down  below  98° 
F.  before  the  thermometer  is  inserted.  If  the  animal 
objects  to  the  insertion,  scratching  her  back  with  a  card 
will  attract  her  attention  and  no  difficulty  be  met. 
Vaseline  may  be  used  on  the  instrument  to  aid  in  its 
insertion. 

The  temperature  should  be  taken  four  times  at  inter- 
vals of.  2  hours,  before  the  injection  of  the  tuberculin. 
The  injection  of  the  tuberculin  is  made  by  the  use  of  a 
well-made  hypodermic  syringe.  The  injection  is  made 
usually  back  of  the  shoulder  blade,  but  may  be  made 
wherever  the  skin  is  loose  and  thin.  The  needle  is 
thrust  through  the  skin  at  right  angles,  but  care  should 
be  taken  not  to  push  it  into  the  muscular  tissue  below. 
A  syringe  with  a  needle  that  slips  on,  rather  than  one 
that  screws  on  to  the  barrel  is  preferable,  since  the 
needle  can  be  inserted  and  the  syringe  then  attached. 
The  needle  should  be  of  15  or  17  wire  guage;  strong 
needles  are  needed  for  this  kind  of  work.  It  is  well  to 
sterilize  the  syringe  before  using  by  placing  it  in  a  pan 
of  cold  water  and  bringing  the  water  to  a  boil. 

Animals  whose  temperatures  are  abnormal,  say  103° 
P..  should  not  be  injected,  neither  is  the  test  as  reliable 
when  applied  to  animals  about  to  calve,  or  those  in 
neat  or  to  young  calves  less  than  3  months  old. 

The  dose  of  tuberculin  depends  upon  the  size  of  the 
animal.  That  distributed  under  the  auspices  of  the 
United  States  Department  of  Agriculture  is  diluted, 
ready  for  use  and  requires  2  c  c.  (40  drops)  per  1000 
pounds  live  weight.  The  amount  of  the  commercial 
tuberculin  to  be  used  is  always  stated  on  the  package. 

The  temperature  records  are  commenced  8  to  10  hours 
after  the  injection,  which  is  usually  made  in  the  evening. 


122 


Agricultural  Bacteriology. 


The  taking  of  temperatures  should  be  continued  at  least 
until  18  hours  after  inoculation"  or  until  there  is  a  per- 
manent decline  toward  the  normal. 

The  animals  should  be  kept  in  as  normal  a  condition 
as  possible  during  the  test.  Care  should  be  taken  not 
to  excite  them  as  this  will  cause  the  temperature  to  rise. 
It  is  usually  preferable  to  make  the  test  at  the  time  the 
cattle  are  kept  in  the  stable,  e.  g.,  fall  or  winter.  One 
point  to  which  attention  should  be  especially  directed 
is  the  watering  of  the  animals  during  the  test.  If  an 

Hours    After    Injection. 


10 


12 


14 


16 


18 


20 


107° 


106° 


105° 


I04C 


3/ 


FIG.  15. — TEMPERATURE  CURVES. 

1.  the  temperature  curve  of  a  healthy  animal  after 
injection  with  tuberculin;  2  and  3.  the  tempera- 
ture curves  of  "tuberculous  animals  after  injec- 
tion with  tuberculin.  (After  Moore.) 

animal  drinks  large  amounts  of  cold  water  its  tempera- 
ture is  often  lowered  2°  to  3°  F.  If  the  depression  of 
temperature  should  come  during  the  reaction  fever,  it 
might  lead  to  a  misinterpretation  of  the  results.  Water 
should  be  given  during  the  test,  and  no  trouble  will 
ensue  if  given  in  small  quantities. 

The  increase  in  temperature  in  the  tuberculous  animal 
is  usually  a  number  of  degrees.    In  the  case  of  a  positive 


Tuberculosis.  123 

reaction  the  temperature  begins  to  rise  10-14  hours  after 
injection,  reaches  a  maximum  in  12-14  hours  and  then 
declines  rapidly.  The  maximum  temperature  may 
reach  105°  to  107°  F.,  e.  g.,  3°  to  5°  F.  above  the  average 
normal.  An  animal  is  said  to  have  reacted  and  is  looked 
upon  as  diseased  when  the  maximum  temperature  after 
injection  is  2°  or  more  above  the  average  normal  tem- 
perature before  injection,  or  is  1.5°  F.  above  the  highest 
temperature  taken  before  injection.  The  reaction  fever 
is  often  so  slight  that  one  cannot  decide  positively  from 
this  alone  whether  the  animal  is  to  be  adjudged  dis- 
eased or  not.  In  the  interpretation  of  such  cases  a  full 
knowledge  of  the  conditions  surrounding  the  test,  and 
a  history  of  the  animal  is  of  much  value.  If  many  other 
animals  of  the  herd  have  reacted,  a  less  rise  in  the  case 
of  one  or  more  animals  would  be  classed  as  a  reaction, 
when  it  would  not  be  in  case  no  other  animals  had 
shown  any  signs  of  a  reaction. 

Suspicious  animals  should  be  retested  with  a  larger 
dose  (3  fold)  after  a  period  of  60  days.  Animals  once 
tested  will  not  give  a  proper  reaction  upon  retest  if 
tested  within  a  short  time  after  the  first  injection. 
Sufficient  time  must  elapse  to  permit  elimination  of  the 
first  tuberculin.  Animals  in  the  last  stages  of  the  dis- 
ease often  do  not  react.  The  disease  in  such  animals 
can  usually  be  diagnosed  by  a  physical  examination. 
During  the  incubation  period  of  the  disease  before  any 
diseased  tissue  has  developed,  animals  do  not  react  to 
tuberculin. 

The  purely  mechanical  part  of  the  test  can  be  carried 
out  by  any  intelligent  farmer  capable  of  reading  ac- 
curately a  clinical  thermometer.  The  interpretation  of 
the  test  should,  however,  be  made  only  by  an  experienced 


124  Agricultural  Bacteriology. 

person.  No  farmer  should  fail  to  test  his  herd  because 
a  veterinarian  is  not  to  be  obtained  or  because  of  the 
expense  of  employing  one.  The  tuberculin  can  be  pur- 
chased of  reputable  firms  at  a  cost  of  15  to  25  cents  per 
dose.  The  instruments  need  not  cost  over  five  dollars. 
The  work  can  be  done  during  the  times  when  the  farm 
work  is  least  pressing. 

The  advantage  of  being  able. to  test  one's  own  animals 
is  very  great,  since  retests  can  be  made  on  suspicious 
animals  and  animals  to  be  brought  into  the  herd,  tested. 
If  some  one  must  be  employed  to  make  those  tests  at  ir- 
regular times,  the  testing  is  likely  to  be  neglected  and 
because  of  this  neglect,  the  farmer  may  fail  to  free  his 
herd  from  the  disease  or  may  introduce  it  by  the  pur- 
chase of  a  cow  supposed  to  be  healthy. 

Reasons  for  testing  the  herd.  Every  farmer  should 
determine  the  condition  of  his  herd  for  its  own  sake 
because  delay  means  increased  loss  through  diminished 
production  of  diseased  animals,  through  further  spread 
of  the  disease  in  the  herds,  and  through  death  of  animals 
before  the  normal  time.  From  the  standpoint  of  duty 
to  himself  and  to  society,  he  should  see  that  his  herd  is 
healthy.  This  can  be,  done  only  by  the  use  of  the  tuber- 
culin test. 

Some  states  have  passed  laws  requiring  compulsory 
testing,  and  for  animals  found  affected,  partial  remuner- 
ation is  given.  The  methods  of  disposal  of  reacting 
animals  depends  upon  the  state  of  the  disease.  When  the 
carcass  is  affected  only  slightly,  it  is  passed  for  food 
under  Federal  inspection.  If  the  disease  shows  evidence 
of  being  generalized,  the  carcass  is  condemned  and 
tanked  for  fertilizer. 

As  previously  indicated,  it  is  possible  to  raise  healthy 


Tuberculosis.  125 

calves  from  diseased  mothers.  With  valuable  breeding 
stock,  the  loss  caused  by  immediate  slaughter  would  be 
too  great.  The  herd  may  be  separated  into  the  affected 
or  reacting,  and  the  healthy.  The  two  herds  should  be 
kept  in  separate  barns  and  pastures;  the  calves  of  the 
diseased  animals  should  be  removed  at  birth  and  fed  on 
the  milk  of  healthy  animals  or  on  the  milk  of  the  dis- 
eased animals  which  has  been  heated  to  at  least  160°  F. 
so  as  to  destroy  any  tubercle  organisms  it  may  contain. 
It  has  been  shown  many  times  in  Denmark  and  in  this 
country  that  by  this  method  a  diseased  herd  can  be  put 
on  a  healthy  basis  within  a  few  years  and  at  very  slight 
expense.  Any  farmer  who  wishes  to  employ  this  system 
should  apply  to  the  state  authorities  connected  with  the 
control  of  contagious  diseases  of  animals  for  more  de- 
tailed advice.  There  is  no  successful  practical  means 
at  present  of  protecting  cattle  against  tuberculosis  by 
vaccination.  Certain  methods  have  been  widely  adver- 
tised as  efficient,  but  are  not  a  practical  success. 

Tuberculosis  of  swine.  Hogs  acquire  the  disease 
very  easily  by  the  ingestion  of  contaminated  food,  such 
as  skim  milk,  butter-milk,  slime  from  cream  separators, 
or  from  cattle  in  feed  lots.  The  parts  of  the  body  most 
often  affected  are  the  glands  of  the  head,  neck,  and  in- 
testines. The  liver  may  show  large  rounded  nodules, 
yellowish-white  in  color,  or  minute  nodules  in  great 
numbers.  The  spleen  often  shows  large  nodules  and  the 
lungs  many  small  ones. 

Since  the  larger  number  of  hogs  are  sent  to  market  be- 
fore they  are  a  year  old,  the  disease  does  not  usually 
make  such  headway  as  to  cause  any  visible  symptoms. 
The  tuberculin  test  has  been  used  in  the  case  of  hogs, 
but  it  is  much  more  difficult  to  apply  than  with  cattle. 


126  Agricultural  Bacteriology. 

The  temperature  of  the  hog  is  much  more  variable  than 
that  of  the  cow.  During  the  test  the  animal  must  be 
kept  perfectly  quiet,  which  can  be  done  only  by  placing 
it  in  a  narrow  crate  so  that  movement  is  impossible. 

Tuberculosis  of  fowls.  The  disease  in  chickens  and 
other  barnyard  fowl  is  due  to  a  different  variety  of  the 
tubercle  bacillus  than  that  causing  the  disease  in  cattle 
-and  man.  It  has  caused  great  loss  in  many  flocks.  The 
most  important  symptoms  are  emaciation,  although  the 
appetite  is  good.  The  eyes  are  bright,  until  shortly  be- 
fore death,  although  the  fowl  may  be  weak  and  move 
about  but  little.  The  birds  are  often  lame  due  to  the 
disease  in  the  joints. 

Of  the  internal  organs  the  liver  is  most  affected.  At 
first  it  shows  small,  grayish  points,  later,  yellow  patches 
appear. 

Differential  diagnosis.  There  are  some  diseases  of 
cattle  and  sheep  that  are  often  mistaken  for  tuberculosis, 
especially  those  in  which  nodules  are  produced  in  the 
walls  of  the  intestines  by  animal  parasites.  Sheep  are 
affected  with  an  intestinal  disease  known  as  "  nodular 
disease"  which  to  the  uninitiated  might  -be  thought  to 
l)e  tuberculosis,  but  which  is  really  caused  by  a  parasitic 
worm  which  burrows  in  the  wall  of  the  intestine  forming 
:a  greenish  colored  nodule  about  the  size  of  a  pea. 


CHAPTER  XII. 
GLANDERS  AND  TETANUS. 

Glanders  is  one  of  the  important  diseases  of  the  horse. 
It  appears  in  two  forms,  the  one  type  affecting  the 
mucous  membranes  being  called  glanders,  while  that 
which  affects  the  lymphatic  system  of  the  skin  is  called 
farcy.  The  disease  is  primarily  one  affecting  horses, 
mules,  and  asses,  but  dogs  and  cats  may  acquire  it  by 
eating  glandered  meat.  Man  may  also  be  affected,  gen- 
erally acquiring  the  disease  from  horses.  It  is  an  es- 
pecially fatal  trouble  in  man. 

Distribution  of  the  disease.  Glanders  is  found  in 
nearly  all  parts  of  the  world.  Australia  is  said  to  be 
free  from  it.  The  congregation  and  transportation  of 
large  numbers  of  horses,  as  is  necessary  in  war  opera- 
tions has  been  instrumental  in  spreading  the  disease 
widely  through  the  world.  During  and  after  the  civil 
war  its  distribution  was  very  rapid  in  this  country  due 
to  the  sale  of  horses  and  mules  by  the  government.  In 
the  Mexican  war,  it  was  introduced  into  Mexico  by  the 
American  cavalry. 

The  disease  is  more  often  found  in  large  stables  than 
on  the  farm.  In  lumber  camps,  on  the  ranges,  and  in 
the  cities,  it  is  constantly  present.  Farmers  who  buy 
animals  from  such  places  are  likely  to  bring  the  disease 
onto  the  farm.  There  are  certain  conditions  that  pre- 
dispose the  animal  to  the  trouble  such  as  unsanitary 
surroundings  in  the  stable  and  overwork. 

A  horse  may  be  in  good  flesh  and  be  able  to  stand 
work  and  yet  have  the  disease  in  a  chronic  form  for 


128 


Agricultural  Bacteriology. 


years.  It  is  through  the  purchase  of  such  an  animal  as 
this  that  the  disease  is  brought  onto  the  farm,  such 
animals  also  serving  to  spread  the  trouble  through  the 
infection  of  mangers  and  watering  troughs. 


FIG.  1 6.— GLANDERS. 

Sores  formed  by  the  breaking  of  the  farcy  buds. 
Note  the  swollen  condition  of  the  leg.  (After 
Reynolds.) 

Symptoms  of  the  disease.  The  acute  form  of  the  dis- 
ease is  rare  in  the  horse  but  common  in  the  mule  and 
ass.  In  the  chronic  form  the  development  is  usually 
slow  and  insidious.  There  is  generally  a -discharge  of 


Glanders  and  Tetanus.  129 

a  sticky  fluid  sometimes  streaked  with  blood  from  one  or 
both  nostrils.  The  animal  may  be  lame  and  may  cough. 
In  glanders  of  the  skin  (farcy)  nodules  which  are 
called  farcy  buds  are  found  in  the  skin  and  in  the 
adjacent  tissue.  They  vary  in  size  from  that  of  a  hemp- 
seed  to  that  of  an  egg.  These  nodules  break  and  form 
running  sores  on  the  surface  of  the  body,  the  discharge 
being  yellowish  and  sticky.  The  nodules  usually  appear 
on  the  legs  and  on  the  head.  The  sores  often  heal  but 
leave  a  permanent  scar. 

Tissues  affected  by  the  disease.  In  chronic  glanders 
the  changes  in  the  tissues  are  found  in  the  air  passages, 
the  lungs,  lymph  glands  and  skin.  Small  nodules  may 
form  on  the  upper  part  of  the  septum  of  the  nose.  The 
nodules,  which  are  translucent  and  grayish  in  color,  may 
break  and  form  ulcers  which  destroy  the  surrounding 
tissue  to  a  greater  or  less  extent,  a  perforation  in  the 
bony  nasal  partition  may  even  be  produced.  There  are 
found  in  the  lower  air  passages  and  in  the  lungs  nodules 
resembling  very  much  those  of  tuberculosis.  They  are 
pearl-gray  in  color,  usually  have  a  yellowish  spot  in  the 
center  due  to  the  death  of  the  tissue.  The  nodules  are 
found  both  on  the  surface  of  the  lung  and  in  the  lung 
tissue.  Similar  nodules  are  also  found  in  the  spleen 
and  less  often  in  the  liver  and  kidneys. 

Care  should  be  exercised  in  the  handling  of  suspected 
horses  as  the  disease  is  easily  transmitted  to  man.  The 
symptoms  in  the  human  being  are  much  the  same  as  in 
the  horse,  sores  forming  on  the  hands  and  in  the  eyes 
and  nose.  Death  usually  takes  place  in  two  to  four 
weeks  although  the  disease  may  become  chronic.  Treat- 
ment is  of  little  avail. 


130  Agricultural  Bacteriology. 

Mallein  test.  Glanders  can  often  be  recognized  by  a 
physical  examination  on  account  of  the  characteristic 
sores  in  the  nose.  The  horse  is  subject  to  nasal  diseases 
that  may  be  mistaken  for  glanders.  When  the  disease 
can  not  be  diagnosed  by  the  physical  examination,  re- 
course may  be  had  to  the  mallein  test  which  is  similar 
to  the  tuberculin  test. 

Mallein  is  prepared  in  the  same  manner  as  is  tuber- 
culin by  growing  the  glanders  bacillus  in  glycerin  broth. 
The  manner  of  applying  the  test  is  also  similar  to  the 
method  followed  in  the  tuberculin  test.  The  mallein  is 
injected  beneath  the  skin  and  a  series  of  temperatures 
taken  both  before  and  after  the  injection  is  made.  A  few 
hours  after  the  injection  of  the  mallein  there  appears 
at  the  point  of  inoculation,  a  hot  inflammatory  swelling, 
which  in  a  glandered  horse  is  very  painful,  and  con- 
tinues to  increase  in  size  for  twenty-four  to  thirty-six 
hours.  This  persists  for  several  days,  gradually  disap- 
pearing in  eight  to  ten  days.  With  healthy  horses  a 
small  swelling  is  produced  at  the  point  of  inoculation 
but  it  disappears  in  twenty-four  hours.  At  the  time 
the  swelling  appears  the  diseased  animal  is  dull, 
breathes  rapidly  and  has  a  poor  appetite.  In  healthy 
horses  no  such  effect  is  noted.  In  the  affected  animal 
a  rise  in  temperature,  from  2  to  2.5°  F.,  occurs  in  the 
course  of  eight  hours,  reaching  its  maximum  in  ten  to 
fifteen  hours.  The  high  temperature  persists  for  twen- 
ty-four to  forty-eight  hours  instead  of  only  a  few  hours 
as  in  the  tuberculin  test.  In  healthy  horses  there  is  no 
rise  in  temperature.  The  test  is  not  quite  so  reliable  as 
the  tuberculin  test  for  some  diseased  animals  do  not 
react  to  the  mallein  test.  Any  animal  that  reacts  to  the 
test  is  certain  to  have  glanders. 


Glanders  and  Tetanus.  131 

In  most  of  the  states  glandered  horses  are  destroyed 
by  the  health  authorities  whenever  they  are  detected. 
The  farmer  should  protect  his  horses  against  glanders 
by  not  allowing  them  to  come  in  contact  with  strange 
horses,  especially  if  there  is  any  reason  to  believe  that 
the  animals  may  be  affected.  If  an  animal  is  purchased 
from  a  sale-stable  or  from  a  range,  it  is  well  not  to  bring 
it  in  contact  with  the  farm  horses,  until  it  is  certain 
that  it  is  not  affected  with  the  chronic  type  of  the  dis- 
ease. The  use  of  the  public  watering  trough  and  public 
stables  is  often  a  means  of  infecting  a  healthy  animal.  A 
stable  in  which  a  diseased  horse  has  been  kept  should 
be  disinfected.  The  glanders  organism  does  not  form 
spores,  hence  is  easily  killed. 

TETANUS. 

Tetanus  or  lockjaw  as  it  is  often  called,  is  a  disease 
that  appears  most  often  in  the  horse  and  mule.  It  may 
however  affect  any  of  the  domestic  animals  and  also 
man.  Tetanus  occurs  in  all  parts  of  the  world,  most 
frequently  in  the  warmer  regions. 

The  organism  causing  the  disease  is  an  anaerobic  one, 
the  real  home  of  which  is  in  the  soil.  The  disease  is 
not  a  directly  contagious  one,  i.  e.,  one  animal  does  not 
acquire  it  from  another.  The  infection  takes  place 
through  a  wound,  especially  one  into  which  dirt  is 
carried.  A  wound  which  bleeds  freely  is  less  dangerous 
than  one  that  does  not  as  the  organisms  are  likely  to  be 
washed  out.  A  contused  lacerated  wound  is  especially 
dangerous  as  the  opportunity  for  admission  of  dirt  is 
increased.  Wounds  caused  by  rusty  and  dirty  nails  are 
often  a  way  in  which  the  bacteria  are  introduced  into 
the  body. «  The  disease  may  follow  an  operation,  such  as 


132  Agricultural  Bacteriology. 

the  docking  of  horses,  the  castration  of  colts,  and 
through  the  infection  of  the  umbilical  cord  of  colts. 

Symptoms.  The  organism  grows  only  at  the  point 
of  introduction.  It  produces  one  of  the  most  powerful 
poisons  known.  This  is  absorbed  and  is  carried  to  all 
parts  of  the  body  and  its  action  on  the  nerves  causes 
the  characteristic  symptoms,  of  spasms  in  various  mus- 
cles. The  muscles  of  the  throat  and  jaw  are  often 
paralyzed,  giving  rise  to  the  common  name  of  the  dis- 
ease, lockjaw.  The  muscles  of  the  neck  may  be  in- 
volved, causing  the  head  to  be  held  in  a  stiff  outstretched 
manner.  Those  of  the  back  and  tail  are  also  affected. 

On  post-mortem  examination  no  marked  lesions  are 
found.  The  disease  is  usually  fatal  in  sheep  and  in  hogs ; 
about  75  per  cent  of  the  horses  affected  die.  The  dura- 
tion of  the  disease  in  the  horse  may  be  but  a  few  days  or 
it  may  continue  for  several  weeks. 

Preventive  measures.  A  preventive  and  to  some  ex- 
tent a  curative  treatment  has  been  developed  in  the 
tetanus  antitoxin.  This  antitoxin  is  prepared  in  the 
same  manner  as  that  used  for  the  prevention  and  cure 
of  diphtheria.  A  horse  is  injected  with  a  small  amount 
of  the  filtrate  of  a  culture  of  the  tetanus  organism  in 
broth.  This  contains  the  same  poison  that  the  organism 
produces  in  the  body  of  the  animal.  A  very  small  dose 
must  be  given  at  first.  The  horse  soon  recovers  from 
the  effect  of  the  injection  and  a  larger  dose  is  then  given. 
The  treatment  is  continued  for  some  time  with  larger 
and  larger  doses  of  the  poison.  Meanwhile  the  animal 
is  producing  a  substance  in  its  body  to  counteract  the 
poison  that  has  been  given  it.  This  process  of  forming 
the  antitoxin  does  not  cease  when  enough  has  been  made 
to  neutralize  the  amount  of  poison  given,  but  an  excess 


Glanders  and  Tetanus.  133 

is  made  and  is  found  in  the  blood  of  the  animal.  If 
some  of  the  blood  can  be  carried  to  an  animal  that  has 
just  begun  to  show  symptoms  of  tetanus,  the  antitoxin 
contained  in  it  will  neutralize  the  poison  that  is  being 
formed  and  thus  tide  over  the  time  until  the  suffering 
animal  can  make  its  own  antitoxin.  This  transfer  of 
the  protecting  substance  is  done  by  drawing  a  quantity 
of  blood  from  the  immunized  animal,  allowing  it  to  clot 
and  collecting  the  serum  which  comprises  the  commercial 
product.  The  antitoxin  is  used  in  the  treatment  of  both 
horses  and  man.  In  order  to  protect  an  animal  against 
the  infection  that  may  occur  during  an  operation  a  small 
dose  is  often  given  before  the  operation.  In  vaccination, 
where  a  mild  form  of  the  specific  disease  is  always  pro- 
duced, the  protection  lasts  for  some  time.  The  protec- 
tion afforded  by  antitoxin  endures  for  only  a  short 
time. 

A  large  proportion  of  the  disease  in  human  beings  is 
the  result  of  wounds  produced  by  Fourth  of  July  ac- 
cidents. The  filling  in  many  forms  of  fire  works  is 
earth.  This  may  contain  tetanus  bacilli  which  will  be 
blown  into  the  skin  by  a  premature  explosion  of  a  fire 
cracker  or  other  form  of  fire  works. 


CHAPTER  XIII. 
RABIES. 

Rabies,  or  hydrophobia,  as  it  is  frequently  called,  is  a 
disease  especially  affecting  dogs.  Practically  all  of  the 
domestic  animals  and  many  wild  animals  may,  how- 
ever, contract  the  disease.  Man  is  also  susceptible. 
While  the  disease  is  especially  important  on  account  of 
its  communicability  to  man,  it  is  becoming  of  much 
economic  importance  to  the  farmer  through  the  loss  of 
stock  infected  by  the-  bites  of  rabid  dogs 

So  far  as  is  known  the  disease  is  transmitted  from 
one  animal  to  another  or  from  animals  to  man  only 
through  the  bite  of  a  rabid  animal.  The  tendency  of 
the  dog  to  bite  is  the  explanation  for  the  great  preva- 
lence of  the  disease  in  this  animal.  The  organism  caus- 
ing the  disease  has  never  been  discovered.  Certain 
structures  have  beenx  found  in  parts  of  the  body  that  are 
supposed  to  be  the  real  cause,  although  the  relation  has 
never  been  thoroughly  established. 

Distribution.  The  disease  is  found  in  nearly  all  parts 
of  the  world.  Australia  is  said  to  be  free  from  it.  This 
freedom  is  due  to  the  rigid  enforcement  of  quarantine 
laws  in  regard  to  the  importation  of  dogs.  England 
through  strict  regulations  concerning  the  muzzling  of 
dogs  and  through  her  quarantine  laws  has  practically 
succeeded  in  stamping  out  the  disease.  In  our  own 
country  rabies  is  found  in  every  state.  In  some  sections 


Rabies.  135 

it  is  very  prevalent  while  in  others  it  is  rare.  It  is  un- 
doubtedly on  the  increase  in  many  sections.  This  is 
due  to  the  lack  of  regulations  in  regard  to  the  muzzling 
of  dogs.  Many  people  believe  that  the  muzzling  is  an 
inhumane  practice,  while  still  others  assert  that  rabies 
is  a  myth  and  has  no  existence  except  in  the  minds  of 
the  doctors.  So  long  as  such  ideas  are  held,  rabies  will 
continue  to  exist. 

There  is  probably  no  other  disease  with  which  there 
is  connected  so  many  popular  fallacies  as  with  rabies. 
It  is  currently  believed  that  it  occurs  only  during  that 
part  of  the  summer  known  as  "dog  days."  In  reality 
the  disease  is  as  prevalent  in  winter  as  in  summer  and 
if  it  is  desirable  to  muzzle  dogs  in  July  and  in  August, 
it  is  also  desirable  to  muzzle  them  at  all  times. 

Period  of  incubation.  The  period  of  incubation  of 
rabies  is  about  forty  days  in  man,  in  the  horse  from 
twenty-eight  to  fifty-six  days,  in  the  dog  from  twenty- 
one  to  forty  days.  The  period  of  incubation,  however, 
may  vary  widely  from  these  averages  as  it  will  depend 
on  the  location  and  severity  of  the  bite.  The  part  of 
the  body  in  which  the  organism  seems  to  grow  is  the 
nervous  system.  The  symptoms  of  the  disease  are  not  ap- 
parent until  the  brain  is  affected.  The  time  required  for 
the  organism  to  reach  the  brain  depends  on  the  distance 
of  the  bite  from  the  brain,  thus  the  symptoms  appear 
more  quickly  when  the  bite  is  on  the  face  than  when  it  is 
on  the  limbs.  The  length  of  the  period  of  incubation  is 
also  dependent  on  the  severity  of  the  bite.  Where  a 
slight  wound  is  inflicted,  the  symptoms  will  not  as  a  rule 
follow  so  soon  as  if  several  wounds  had  been  made. 

Symptoms.  Two  forms  of  the  disease  are  known,  the 
dumb,  and  the  furious  type,  so  called  on  account  of  the- 


136  Agricultural  Bacteriology. 

nature  of  the  symptoms  noted.  In  the  rabbit  the  dumb 
type  is  most  usual ;  in  the  dog  it  is  very  rare.  The  symp- 
toms of  rabies  appear  slowly.  With  the  furious  type  of 
the  disease,  the  animal  is  usually  more  nervous  than  nor- 
mal and  more  affectionate,  or  it  may  be  dull  and  try  to 
avoid  people.  The  nervousness  increases  until  the  ani- 
mal is  unable  to  rest.  It  may  become  delirious  and  snap 
at  the  air.  The  itching  of  the  tissue  at  the  point  of  in- 
oculation causes  the  dog  to  lick  the  wound  or  even  to  bite 
itself.  The  nervousness  may  be  so  great  that  the  dog 
leaves  home,  and  starts  on  a  wandering  trip  which  may 
last  for  several  days,  usually  returning  home  in  an  ex- 
hausted condition.  During  this  absence  from  home  is  the 
time  of  greatest  danger,  for  the  dog  then  comes  in  con- 
tact with  other  animals.  The  rabid  dog  does  not  go  out 
of  its  way  to  bite,  as  is  frequently  stated,  but  any  object 
or  other  animal  that  is  in  its  way  is  very  likely  to  be 
snapped  at.  The  animal  that  is  most  usually  bitten  is 
another  dog.  In  this  way  the  disease  is  spread,  as  on 
such  a  trip  the  mad  dog  may  infect  a  large  number  of 
dogs. 

The  animal  may  die  while  away  from  home.  More 
often  it  reaches  home  in  a  pitiable  condition,  and  often 
the  owner  may  be  bitten  in  seeking  to  relieve  the  animal. 
The  greatest  care  should  be  exercised  in  handling  any 
•dog  suspected  of  rabies.  As  the  disease  progresses,  cer- 
tain parts  of  the  body  become  paralyzed,  the  muscles  of 
the  throat  generally  being  the  first  to  be  affected.  This 
has  led  to  another  popular  fallacy,  namely  that  a  rabid 
animal  has  a  great  fear  of  water,  often  going  into  fits  at 
the  sight  of  water.  This  fallacy  has  given  to  the  disease 
the  name  ''hydrophobia,"  meaning  fear  of  water.  The 
.animal  is  unable  to  swallow,  and  in  making  an  attempt 


Rabies.  137 

to  do  so  is  often  thrown  into  convulsions.  The  animal 
will  take  water  as  long  as  it  is  able  to  swallow  anything. 
The  paralysis  gradually  extends  and  death  usually  takes 
place  in  four  or  five  days  after  the  first  symptoms  are 
noted. 

In  the  dumb  type  the  nervousness  is  not  present,  the 
first  symptom  is  usually  paralysis  of  the  muscles  of  the 
throat.  This  often  leads  the  owner  to  think  the  dog  is 
choking  and  an  effort  may  be  made  to  remove  the  sus- 
pected object  by  inserting  the  hand  into  the  mouth. 
This  is  a  very  dangerous  thing  to  do  for  the  saliva  is  in- 
fectious and  if  the  hand  should  be  scratched  in  the 
operation  there  is  danger  that  rabies  may  develop.  Even 
the  licking  of  the  hand  by  a  rabid  animal  may  serve  to 
infect  a  person  if  there  is  any  sore  or  abrasion  of  the  skin. 
The  extent  of  the  danger  from  bites  depends  to  a  large 
degree  upon  the  location  of  the  bite.  If  the  teeth  of  the 
dog  pass  through  the  clothing,  the  saliva,  which  carries 
the  virus,  will,  generally,  be  wiped  off.  The  disease  will 
be  far  less  likely  to  follow  than  if  the  bite  is  on  an  un- 
protected part  as  the  face  or  hands.  In  like  manner  a 
long-haired  dog  is  more  protected  than  a  short-haired 
one.  As  previously  stated  the  danger  also  depends  upon 
the  severity  of  the  bites.  People  bitten  by  rabid  wolves 
more  often  develop  the  disease  than  those  bitten  by  dogs 
because  the  bites  are  likely  to  be  more  extensive.  An- 
other fallacy  connected  with  rabies  is  that  if  persons  or 
animals  are  bitten  by  any  dog,  they  are  likely  to  become 
rabid  should  thejiog  contract  the  disease  at  any  future 
time.  There  is,  of  course,  absolutely  no  foundation  for 
this  impression,  for  the  disease  is  transmitted  only  by 
an  animal  that  is  diseased  at  the  time  the  wound  is  in- 
flicted. 


138  Agricultural  Bacteriology. 

The  body  of  a  dog  that  has  died  of  rabies  shows  no 
marked  changes  on  post-mortem  examination.  The  stom- 
ach is  likely  to  contain  foreign  objects,  such  as  grass, 
sticks,  etc. 

Treatment  of  rabies.  If  the  disease  develops  until 
symptoms  are  apparent,  nothing  can  be  done  and  death 
is  certain  to  follow.  In  human  beings  the  death  is  one 
of  the  most  horrible  than  can  be  imagined.  However,  if 
treatment  is  begun  early  enough  the  disease  can  be  pre- 
vented. The  basis  of  the  treatment  is  exactly  the  same 
as  in  the  cases  of  anthrax  and  black  leg.  A  weakened 
form  of  the  virus  is  used.  If  rabbits  are  inoculated  with 
a  portion  of  the  spinal  cord  or  brain  of  a  rabid  animal,, 
they  will  usually  die  from  the  disease  in  fifteen  to  twenty 
days.  If  repeated  inoculations  are  made  from  one  ani- 
mal to  another,  the  virulence  of  the  causal  organism  in- 
creases ,until  the  rabbits  will  die  in  six  or  seven  days. 
The  virulence  can  not  be  farther  increased  and  the  virus 
is  said  to  have  a  fixed  strength.  The  spinal  cord  of  a 
rabbit  that  has  died  after  inoculation  with  such  a  fixed 
virus  is  removed  and  placed  in  a  dry  atmosphere,  the  re- 
sulting desiccation  weakens  the  organism  gradually.  A 
person  applying  for  treatment  is  given  a  sub-cutaneous 
inoculation  with  a  suspension  in  water  of  a  cord  that  has 
been  dried  for  fourteen  days;  on  the  following  day  the 
inoculation  is  made  with  a  cord  that  has  been  dried  for 
a  shorter  period  of  time.  Within  a  week  or  ten  days  the 
inoculation  is  made  with  a  cord  that  has  just  been  re- 
moved from  the  animal,  and  which,  of  course,  contains 
the  unweakened  virus.  The  treatment,  which  was  dis- 
covered by  the  French  bacteriologist,  Pasteur,  has  re- 
sulted in  the  saving  of  hundred  of  lives  and  has  robbed 
the  disease  of  many  of  its  terrors.  The  treatment  is  em- 


Rabies.  139 

ployed  only  with  human  beings,  although  animals  could 
be  treated  but  the  expense  is  too  great. 

It  is  noteworthy  that  the  protective  treatment  can  be 
applied  in  the  case  of  rabies  several  days  after  the  bite 
is  inflicted,  an  unusual  condition  with  reference  to  im- 
munization. On  account  of  the  time  and  expense  con- 
nected with  the  preventive  treatment,  it  is  desirable  to 
know  with  certainty  that  the  suspected  animal  really  has 
rabies.  This  can  be  determined  with  certainty  only  by 
keeping  the  dog  that  inflicted  the  bite  under  observation. 
If  the  animal  is  rabid,  a  definite  diagonsis  can  be  made 
from  the  symptoms,  and  death  is  certain  to  follow.  If  the 
dog  has  bitten  persons,  it  is  especially  desirable  that  it 
should  not  be  killed  for  the  delay  in  determining  whether 
the  animal  was  actually  rabid  or  not  may  be  sufficient  to 
allow  the  disease  to  make  such  headway  that  treatment 
will  be  of  no  value  in  preventing  the  disease.  Until  re- 
cently the  diagnosis  was  made  by  the  inoculation  of  a 
portion  of  the  spinal  cord  into  rabbits.  A  more  rapid 
method  is  now  employed,  a  definite  portion  of  the  brain 
is  examined  microscopically  and  within  twenty-four 
hours  the  diagnosis  can  be  made,  while  with  the  old 
method  at  least  two  weeks  were  required. 

A  very  unsatisfactory  condition  in  all  methods  of  diag- 
nosis in  the  laboratory  exists.  If  the  rabbits  inoculated 
succumb  to  rabies  or  if  the  peculiar  bodies  characteristic 
of  the  disease  are  found  in  the  brain  of  the  suspected 
animal,  it  is  certain  that  rabies  is  present.  If  the  bodies 
are  not  found,  it  is  not  certain  that  the  animal  was  free 
from  the  disease.  Again,  the  rabbits  inoculated  may  not 
die  from  the  disease  for  a  much  longer  period  than  the 
average,  so  late,  indeed,  that  preventive  treatment  may 
be  of  no  value,  if  it  is  not  begun  until  the  diagnosis  is 


140  Agricultural  Bacteriology. 

made  by  means  of  animal  inoculation.  These  things 
-emphasize  the  importance  of  not  killing  the  suspected 
animal,  but  to  secure  it,  and  watch  the  progress  of  the 
•disease.  If  rabies  is  present  the  animal  is  certain  to  die 
with  well  marked  symptoms  which  can  not  be  mistaken. 
If  the  dog  is  suffering  from  various  other  troubles  that 
cause  it  to  be  nervous,  or  if  it  has  inflicted  the  bite 
through  provocation,  an  entirely  different  history  will 
result.  Every  effort  should  be  made  to  secure  the  dog 
that  has  bitten  other  dogs,  animals,  or  persons.  If  the 
suspected  dog  has  been  killed,  the  head  should  be  re- 
moved and  sent  to  a  laboratory  for  examination ;  most  of 
the  laboratories  connected  with  the  state  boards  of  health 
are  equipped  for  such  work.  Care  should  be  taken  not 
to  injure  the  brain  else  diagnosis  may  be  impossible. 

The  wounds  made  by  a  suspected  animal  should  be 
cauterized  immediately  to  destroy  the  virus  possibly  pres- 
ent. This  can  be  done  by  the  use  of  strong  carbolic  or 
nitric  acid  or,  if  neither  of  these  are  available,  by  the  use 
of  a  hot  iron.  Only  about  sixteen  per  cent  of  people 
bitten  by  rabid  animals  develop  rabies  and  this  is  greatly 
reduced  when  the  wounds  are  properly  treated. 

The  preventive  treatment  is  given  in  Pasteur  Institutes 
which  have  been  established  in  the  various  cities.  Some 
of  the  states  have  such  institutes  in  connection  with  the 
laboratories  of  the  boards  of  health.  Recently  farther 
improvement  has  been  developed  so  that  the  vaccine  can 
be  sent  by  mail  to  the  resident  physician,  who  admin- 
isters it.  In  this  way  a  person  can  take  the  treatment 
at  home  and  at  much  less  expense  than  formerly. 

Rabies  in  other  animals.  Next  to  dogs,  cattle  seem 
to  be  most  frequently  affected,  probably  because  rabid 
dogs  have  more  opportunity  to  bite  them  than  any  other 


Rabies.  141 

domestic  animal  except  other  dogs.  Cattle  are  most  fre- 
quently bitten  on  the  hind  legs,  hips  and  lower  jaw. 
About  twenty-five  to  thirty  per  cent  of  those  bitten  de- 
velop the  disease.  The  symptoms  are  very  similar  to 
those  described  in  the  dog.  The  furious  type  is  more 
common  than  the  dumb.  The  first  symptoms  are  loss  of 
appetite,  of  rumination  and  of  milk  secretion.  Increased 
nervousness  is  shown  by  the  bellowing,  pawing,  and  a 
tendency  to  attack  other  animals.  On  account  of  the  in- 
creased amount  of  saliva,  there  is  a  constant  frothing  at 
the  mouth.  The  animal  becomes  stiff  and  unsteady  in 
its  gait.  The  temperature  is  not  above  normal.  Death 
results  from  paralysis. 

Quite  similar  symptoms  may  be  noted  in  other  dis- 
eases in  which  the  brain  is  affected  as  for  example  in 
lock  jaw,  anthrax,  and  spinal  meningitis. 

Horses,  sheep  and  hogs  are  often  bitten  by  rabid  dogs. 
The  symptoms  are  usually  those  of  the  furious  type  of 
the  disease.  A  rabid  horse  or  hog  may  bite  other  animals 
or  man  and  cause  the  spread  of  the  disease. 


CHAPTER  XIV. 

ACTINOMYCOSIS,  GARGET,  COWPOX,  AND  CON- 
TAGIOUS ABORTION. 

Actinomycosis  or  lumpy  jaw  as  it  is  commonly  called, 
is  a  disease  of  cattle  although  horses,  sheep,  hogs,  and 
•dogs  may  be  affected.  Man  is  also  subject  to  the  disease. 
The  cause  of  the  disease  is  not  one  of  the  bacteria  but  an 
organism  much  like  a  mold.  The  disease  is  not  a  highly 
important  one  as  only  about  one  out  of  sixteen  hundred 
.animals  are  affected  with  it.  Tuberculosis  is  at  least 
fifty  times  as  prevalent  as  is  actinomycosis  and  yet  in 
many  places  the  latter  disease  has  made  more  of  an  im- 
pression on  the  popular  mind  than  has  tuberculosis. 
The  reason  is  that  the  changes  which  tuberculosis  pro- 
duces are  hidden,  while  those  of  actinomycosis  are  usually 
evident  on  the  surface  of  the  body  in  the  form  of  a  lump 
on  the  jaw.  Animals  rarely  die  of  the  disease. 

Actinomycosis  is  not  a  contagious  disease  since  one 
animal  does  not  acquire  the  disease  from  another.  The 
organism  that  causes  the  trouble  is  supposed  to  grow  on 
barley  and  other  grains.  It  enters  the  body  through  a 
wound  in  the  mouth,  through  a  hollow  tooth  or  it  may 
"be  inhaled. 

Symptoms.  The  first  symptom  is  a  slight  swelling  in 
the  region  of  the  head  or  throat.  The  swelling  gradually 
increases  in  size  and  is  hard  and  dense.  It  may  break 
and  discharge  a  thick  yellow  pus.  The  opening  may  heal 
temporarily  only  to  break  later  and  discharge  again. 


Actinomycosis.  143 

The  discharge  may  be  on  the  outside  or  into  the  mouth 
or  throat.  The  sore  at  the  point  of  discharge  may  be- 
come very  large  and  have  the  appearance  of  a  head  of 
cauliflower.  The  growth  of  the  tumor  may  continue  for 
years,  death  being  caused  because  of  its  interference  with 
breathing  or  swallowing.  The  tongue  is  sometimes  in- 
volved, in  which  case  the  disease  is  often  given  the  name 


PIG.  17. — ACTINOMYCOSIS. 

'The  spongy  condition  of  the  jaw  bone  was  produced 
by  the  growth  of  the  fungus. 

of  "wooden  tongue."  The  organism  may  invade  the 
bony  part  of  the  jaw,  causing  the  bone  to  become  spongy 
and  enlarged,  while  the  teeth  may  fall  out. 

Lesions.  The  lesions  of  actinomycosis  may  occur  in 
various  other  parts  of  the  body  than  about  the  head.  In 
the  lungs  nodules  are  often  formed  that  are  very  similar 
to  the  nodules  found  in  tuberculosis  of  the  lungs.  They 
vary  in  size  from  mere  specks  to  that  of  a  pea.  Still 
other  organs,  as  the  spleen,  liver,  and  udder  may  contain 
the  nodules  produced  by  the  growth  of  the  organism. 
The  pus  discharged  from  the  actinomycotic  nodules  i* 


144  Agricultural  Bacteriology. 

yellowish  and  contains  minute  yellow  granules,  often 
called  sulphur  grains.  These  are  masses  of  the  causal 
organism. 

Treatment.  The  disease  is  one  that  yields  quite  read- 
ily to  treatment.  The  most  successful  remedy  is  potas- 
sium iodide  which  is  given  in  water  as  a  drench.  The 
dose  is  from  1.5  to  2.5  drams  per  day.  The  treatment 
can  not  be  maintained  continuously  for  a  long  time  as  the 
drug  affects  the  animal  unfavorably,  causing  the  eyes  to 
run,  the  skin  to  become  dry  and  rough,  and  a  loss  of 
appetite.  "When  these  troubles  manifest  themselves  the 
medicine  must  be  stopped  for  a  few  days  and  then  begun 
again.  Three  to  six  weeks  are  required  to  effect  a  cure. 
All  animals  do  not  respond  to  this  treatment.  Iodine 
should  never  be  given  to  milch  cows  as  it  is  given  off  in 
the  milk.  It  also  decreases  the  flow  of  milk  or  may  stop 
it  entirely.  It  is  also  likely  to  cause  abortion. 

Man  does  not  acquire  the  disease  directly  from  cattle 
but  is  infected  in  the  same  manner  as  are  cattle  through 
wounds  in  the  mouth.  The  meat  of  animals  that  have 
the  disease  in  a  localized  form  is  fit  for  human  food  and 
is  passed  by  the  inspectors  in  the  slaughter-houses. 

GARGET. 

Inflammation  of  the  udder  is  known  by  various  names 
as  garget,  mastitis  or  mammitis.  The  trouble  is  charac- 
terized by  the  production  of  a  fever  and  a  swelling  of 
the  gland  with  more  or  less  change  in  the  nature  of  the 
milk.  Catching  cold  in  the  udder  or  an  injury  are  often 
responsible  for  the  trouble.  Animals  differ  widely  in 
their  susceptibility  to  udder  troubles.  With  some,  lying 
on  a  cold  concrete  floor  is  sufficient  to  cause  trouble.  An 
injury  serves  to  introduce  some  of  the  bacteria  of  the  skin 


Garget.  145 

or  of  the  milk  ducts  into  the  udder  tissue  where  they 
cause  inflammation.  Such  physiological  troubles  are 
usually  confined  to  a  single  animal,  and  the  swelling  and 
fever  are  generally  temporary.  In  well  developed  cases 
the  milk  is  likely  to  contain  flakes  of  slimy  clotted  ma- 
terial. If  the  inflammation  persists,  the  milk  secretion 
may  cease  altogether  and  only  a  yellowish  liquid  be  ob- 
tained. If  the  attack  is  of  short  duration,  no  permanent 
harm  is  likely  to  result,  the  normal  flow  of  the  diseased 
quarter  may  be  restored  during  the  same  lactation  period 
or  at  the  beginning  of  the  next.  A  prolonged  attack  is 
likely  to  cause  a  loss  of  the  quarters  involved. 

A  much  more  serious  type  of  garget  is  that  known  as 
infectious  or  contagious  garget,  which  is  caused  by  cer- 
tain bacteria  which  are  able  to  grow  in  the  udder  and 
cause  serious  trouble.  This  form  is  much  more  import- 
ant than  that  caused  by  cold  or  wounds  as  it  is  very  likely 
to  spread  from  one  animal  to  another.  The  milker  is 
usually  the  cause  of  the  spread  of  the  trouble  in  the  herd. 
An  animal  that  has  garget  in  any  form  should  be  milked 
last  or  the  hands  should  be  washed  in  a  disinfectant 
such  as  can  easily  be  made  by  the  use  of  the  corrosive 
sublimate  tablets  that  can  be  obtained  at  any  drug  store. 
It  is  also  advisable  to  remove  the  animal  from  the  stable. 
Through  carelessness  a  large  part  of  the  herd  may  be- 
come infected. 

The  milk  from  animals  having  inflammation  of  the 
udder,  no  matter  how  slight  it  may  be,  should  not  be 
mixed  with  that  from  healthy  animals.  It  should  be 
thrown  away. 


146  Agricultural  Bacteriology. 

COWPOX. 

Small  pox  in  man  finds  its  counterpart  in  diseases  of 
similar  nature  in  the  cow,  horse,  and  sheep.  There  is  ap- 
parently some  relation  existing  between  human  small  pox 
and  cow  pox,  as  inoculations  from  man  to  the  cow  and 
from  cow  to  man  can  be  made.  The  disease  in  sheep  is 
limited  to  sheep  alone,  not  even  being  transmitted  to 
goats. 

The  lesions  of  cow  pox  appear  on  the  udder  and  teats. 
The  first  symptom  is  a  tenderness  of  the  skin,  followed 
by  the  appearance  of  small  reddish  spots,  which  develop 
into  vesicles  or  blisters  filled  with  a  clear  liquid.  Later 
(tho  contents  become  more  like  pus.  The  pustules  be- 
come darker  in  color  and  drier  until  nothing  remains  but 
a  dry  scab  that  drops  off.  The  duration  of  the  disease  is 
about  twenty  days. 

It  is  not  a  serious  disease  as  far  as  the  herd  is  con- 
cerned. With  milch  cows  it  may  cause  a  great  deal  of 
inconvenience  in  milking.  The  vesicles  are  broken  by 
the  hand  of  the  milker,  thus  producing  large  sores  on  the 
teats  which  heal  slowly  and  which  make  milking  very 
difficult.  An  effort  should  be  made  to  limit  the  spread 
of  the  trouble  in  the 'herd  by  milking  the  affected  cows 
last,  since  one  of  the  agents  of  distribution  of  the  dis- 
ease in  the  herd  is  the  milker  whose  hands  are  contam- 
inated from  the  ruptured  vesicles.  Nothing  can  be  done 
in  a  curative  way,  but  the  use  of  carbolized  vaseline  on 
the  teats  may  serve  to  make  the  milking  less  difficult  and 
aid  in  healing  the  sores. 

The  milker  may  become  infected  from  the  cow  by  get- 
ting some  of  the  contents  of  the  vesicles  into  a  wound  or 
crack  on  the  hand.  The  trouble  in  man  is  local  and  not 
at  all  serious  unless  the  sores  become  infected  with  pus- 


Contagious  Abortion.  147 

forming  bacteria.  An  attack  of  cow  pox  protects  the 
individual  against  small  pox.  In  fact  the  beginning  of 
modern  vaccination  against  small  pox  was  due  to  an  ob- 
servation made  by  Jenner  that  people  that  became  in- 
fected with  cow  pox  did  not  acquire  small  pox.  Vaccine, 
which  is  used  as  a  preventive  against  small  pox,  is  made 
by  inoculating  calves  with  the  virus  of  cow  pox.  To 
make  the  vaccine  the  scabs,  that  form,  are  removed  and 
ground  with  glycerine.  All  the  processes  are  carried  out 
with  the  greatest  care  in  order  to  avoid  the  contamina- 
tion of  the  vaccine  with  organisms  that  might  be  injur- 
ious to  the  persons  vaccinated. 

CONTAGIOUS  ABORTION. 

The  causes  of  abortion  in  cattle  may  be  divided  into 
three  classes:  (1)  abortion  caused  by  mechanical  injury 
or  as  the  result  of  some  other  disease,  (2)  abortion  due  to 
the  presence  of  large  amounts  of  smut  in  the  feed,  (3) 
abortion  due  to  the  infection  of  the  animal  with  a  spe- 
cific organism.  The  first  two  classes  are  of  interest  to  us 
only  as  they  are  to  be  differentiated  from  the  true  con- 
tagious abortion.  The  cases  of  abortion  belonging  in  the 
first  class  are  sporadic  and  are  caused  by  some  injury, 
such  as  slipping,  falling,  being  hooked,  jammed  or 
kicked.  The  cases  occur  singly  and  no  connection  be- 
tween the  cases  can  be  traced. 

Ergot  or  smut  of  corn  and  other  plants  when  ingested 
has  such  an  effect  on  the  uterus  as  to  cause  the  expulsion 
of  the  fetus.  If  the  cause  is  of  this  nature  a  large  num- 
ber of  cases  of  abortion  are  likely  to  occur  within  a  short 
time  since  all  the  cattle  are  under  the  same  conditions. 
With  a  change  of  feed  the  trouble  disappears.  Some 


148  Agricultural  Bacteriology. 

plants  to  which  cattle  may  have  access  in  the  pasture 
have  a  like  effect  on  the  pregnant  animal. 

Contagious  abortion  or  that  caused  by  micro-organisms 
is  more  prevalent  and  more  important,  since  one  infected 
animal  introduced  into  the  herd  may  serve  to  infect  the 
entire  herd. 

Cause.  The  organism  responsible  for  the  trouble  is 
not  known  with  certainty.  The  disease  is  undoubtedly 
most  often  brought  into  the  herd  through  the  purchase 
of  an  infected  animal.  Once  introduced  it  spreads  from 
one  animal  to  another  in  various  ways.  The  first  case  in 
the  herd  is  not  likely  to  attract  attention  and  hence  op- 
portunity is  offered  for  further  spread.  Much  would  be 
gained  if  every  case  of  abortion  in  the  herd  were  treated 
as  though  it  were  contagious.  The  disease  usually  disap- 
pears from  a  herd  in  two  or  three  years,  in  case  no  new- 
animals  are  brought  into  the  herd  or  young  animals  do 
not  serve  to  perpetuate  the  disease.  This  has  been  sup- 
posed to  indicate  that  an  animal  becomes  immune  after 
two  or  three  consecutive  abortions.  The  abortion  usually 
occurs  between  the  fifth  and  eighth  months  of  the  period 
of  gestation. 

Symptoms.  Shortly  before  the  time  for  the  fetus  to 
be  expelled,  symptoms  are  shown  in  varying  degree  by 
different  animals.  The  vulva  and  surrounding  tissue  is 
swollen  and  a  yellowish  discharge  is  noted.  The  udder 
increases  in  size.  Within  two  to  three  days  delivery 
occurs,  which  is  usually  accomplished  without  trouble. 
If  the  abortion  occurs  during  the  eighth  month  of  preg- 
nancy, the  milk  flow  will  usually  be  quite  normal,  at 
earlier  periods  the  animal  gives  milk  but  a  short  time. 


Contagious  Abortion.  149 

Infection  of  the  animal.  There  are  many  ways  in 
which  the  causal  organisms  may  be  carried  from  the  in- 
fected animal  to  a  healthy  one,  as  by  direct  contact,  soiled 
bedding,  the  attendants,  etc.  A  less  direct  way  is  by  the 
bull  that  has  served  infected  animals  and  later  has  been 
used  with  healthy  cows.  The  bull  is  one  of  the  means 
of  introducing  the  disease  into  the  herd,  either  through 
purchase  or  by  the  use  of  the  bull  of  the  herd  on  in- 
fected cows  or  by  patronizing  bulls  kept  for  public  ser- 
vice. 

Prevention.  Attention  should  be  directed  to  the  con- 
dition of  the  herd  from  which  each  animal  is  purchased. 
If  it  is  not  certain  that  the  herd  is  free  from  the  disease, 
it  may  be  well  to  keep  the  purchased  animals  apart  from 
the  herd  until  after  calving  at  full  time  has  occurred. 
In  order  to  prevent  the  spread  of  the  disease  in  the  herd 
attention  must  be  directed  toward  the  destruction  of  all 
material  that  may  contain  the  organisms.  To  accom- 
plish this,  the  fetus  and  after-birth  should  be  destroyed, 
preferably  by  burning.  The  aborting  animal  should  be 
removed  from  the  herd,  the  stable  disinfected  and  all 
cows  that  may  have  been  exposed  also  disinfected.  The 
animal  should  be  given  vaginal  douches  with  some  disin- 
fecting solution  such  as  one  ounce  of  tincture  of  iodine 
in  one  ounce  of  glycerine,  the  mixture  being  added  to  one 
gallon  of  warm  water.  The  external  genitals,  hind  quar- 
ters, and  tail  should  be  washed  with  a  one  to  one  thou- 
sand solution  of  corrosive  sublimate.  The  douches  and 
external  treatment  should  be  repeated  several  times  and 
the  animal  should  not  be  returned  to  the  herd  as  long  as 
there  is  any  vaginal  discharge. 

All  pregnant  cows  of  the  herd  should  be  treated  by 
washing  the  external  genital  parts  with  corrosive  subli- 


150  Agricultural  Bacteriology. 

mate  and  the  vagina  should  be  cleansed  with  a  suitable 
•antiseptic  solution.  The  bull  may  be  treated  by  wash- 
ing the  external  parts  of  the  sheath  and  the  abdomen 
with  soap  and  water  and  then  with  a  one  to  one  thousand 
solution  of  corrosive  sublimate.  The  sheath  may  be  in- 
jected with  a  one  per  cent  solution  of  carbolic  acid. 

The  disinfection  of  the  stable  should  be  done  as  de- 
scribed in  a  subsequent  chapter.  It  rests  largely  with 
the  owner  as  to  whether  the  disease  persists  or  not.  The 
measures  necessary  to  prevent  the  spread  of  the  trouble 
in  the  herd  may  be  burdensome  and  are  very  likely  to  be 
neglected.  It  is  very  certain  that  the  various  methods 
of  treatment  widely  advertised  rely  for  their  effective- 
ness upon  such  means  as  the  farmer  can  apply  for  him- 
self. 


CHAPTER  XV. 
DISEASES  OF  HOGS. 

The  hog  may  be  affected  by  a  number  of  the  diseases 
that  have  already  been  treated,  such  as  tuberculosis.  By 
far  the  most  important  disease  that  especially  affects  the 
hog  is  hog  cholera.  It  is  probable  that  there  are  two 
and  possibly  three  diseases,  caused  by  different  kinds  of 
organisms  to  which  this  term  is  usually  applied.  The 
veterinarians  have  called  one  of  these  diseases  hog 
cholera,  another  swine  plague,  and  within  recent  yearsy 
it  has  been  found  that  there  is  still  a  third  kind  of  or- 
ganism which  causes  trouble  in  the  hog.  These  diseases 
may  be  discussed  together  since  methods  of  prevention 
are  identical. 

The  knowledge  of  no  other  important  group  of  dis- 
eases of  the  domestic  animals  is  in  such  an  unsatisfac- 
tory condition  as  that  concerning  the  diseases  of  the 
hog.  This  is  true  both  with  reference  to  £he  causal  or- 
ganisms, and  to  methods  of  prevention  by  means  of  vac- 
cine or  serums.  Until  very  recently  no  progress  had 
been  made  in  methods  of  fighting  the  diseases  of  the  hog 
for  twenty  years.  ; 

Distribution.  Hog  cholera  is  supposed  to  have  been 
imported  to  this  country  in  the  hogs  introduced  from 
Europe.  The  first  outbreak  of  which  record  is  had  was 
in  Ohio  in  1833.  Since  that  time  it  has  spread  to  every 
state.  In  the  great  corn  growing  states  it  causes  greater 
annual  losses  than  any  other  disease  of  the  domestic  ani- 


152  Agricultural  Bacteriology. 

mals.     It  is   found   in   England,    Germany,   and   other 
European  countries. 

Symptoms.  The  hog  when  ill  usually  shows  much 
the  same  symptoms,  whatever  the  trouble  may  be.  The 
disease  develops  from  seven  to  fourteen  days  after  in- 
fection occurs.  When  the  disease  appears  in  a  herd, 
some  of  the  animals  are  certain  to  die  after  a  short  ill- 
ness of  a  few  hours,  or  at  longest  a  few  days,  of  acute 
cholera.  Others  show  signs  of  illness  for  a  much  longer 
period  and  some  recover.  The  animal  acts  dumpish,  and 
tries  to  hide.  The  appetite  usually  is  very  good.  The 
skin  of  the  ears,  nose,  abdomen,  and  inside  of  the  thighs 
is  reddened.  "With  chronic  cases  weakness  of  the  limbs, 
•especially  the  hind  legs,  develops  and  the  animal  moves 
with  difficulty. 

Post-mortem  examinations.  The  disease  often  can- 
not  be  diagnosed  with  certainty  from  the  symptoms,  but 
an  examination  of  the  carcass  is  necessary.  In  the  acute 
type  one  of  the  most  common  and  striking  changes  is  in 
the  spleen.  This  organ  is  often  much  enlarged,  soft  and 
very  full  of  blood.  Hemorrhages  are  found  in  various 
parts  of  the  body,  especially  on  the  lining  of  the  abdomen 
and  chest,  and  on  the  inner  wall  of  the  intestine.  The 
intestinal  contents  may  be  surrounded  by  a  blood  clot. 
In  the  chronic  form  the  most  characteristic  lesions  are 
found  in  the  large  intestines  in  the  form  of  ulcers  on  the 
inner  wall.  The  ulcers  may  be  as  large  as  a  hickory  nut 
and  because  of  the  rounded  form  are  called  ''button 
ulcers. ' '  The  death  of  the  tissue  near  the  ulcer  may  be 
so  extensive  as  to  cause  a  perforation  of  the  wall  of  the 
intestine,  thus  giving  an  opportunity  for  the  intestinal 
contents  to  escape  into  the  abdominal  cavity.  Such  a 


Diseases  of  Hogs.  153 

condition  produces  inflammation  (peritonitis),  causing 
death.  In  this  type  the  spleen  is  not  usually  enlarged 
and  the  lungs  are  normal. 

Hogs  are  subject  to  intestinal  troubles  that  are  often 
mistaken  for  cholera,  but  may  be  differentiated  from  it 
through  the  fact  that  they  do  not  spread  to  other  herds. 
The  trouble  may  be  produced  by  unsuitable  food,  such  as 
house  refuse  containing  much  soap.  Often  the  mortality 
with  such  troubles  is  high,  and  the  rapid  death  of  the 


FIG.  18.— HOG  CHOLERA. 

Button  ulcers  on  the  inner  wall  of  the  intestine  in 
a  case  of  chronic  hog  cholera.    (After  Reynolds.) 

animals  causes  the  farmer  to  think  a  contagious  disease 
is  present.  The  term  ''swill-barrel"  cholera  is  often 
used  for  such  outbreaks. 

Prevention.  As  there  is  no  cure  for  the  disease,  the 
owner  must  devote  his  efforts  to  prevention.  The  dis- 
ease may  be  brought  onto  a  farm  in  a  number  of  ways, 
most  frequently,  through  the  purchase  of  animals.  As 
previously  stated  animals  recover  from  the  disease. 
Such  animals  may  harbor  the  disease-producing  bacteria 
in  their  bodies  and  disseminate  them  subsequent  to  ap- 
parent recovery  As  soon  as  such  animals  are  brought 


154  Agricultural  Bacteriology. 

into  a  healthy  herd,  an  outbreak  develops,  since  many 
of  the  animals  of  the  herd  will  be  very  susceptible  to  the 
disease.  The  bacteria  are  given  off  from  the  body  of  the 
affected  hog  in  the  manure  and  are  taken  into  the  body 
of  the  healthy  animal  with  the  food. 

No  animal  should  be  purchased  from  a  herd  in  which 
hog  cholera  has  been  present  during  the  previous  year. 
Animals  purchased  should  be  kept  in  quarantine  when 
first  brought  onto  the  farm,  and  then  placed  with  a  small 
part  of  the  herd.  If  these  exposed  animals  all  remain 
healthy  after  two  to  three  weeks,  it  is  safe  to  place  the- 
purchased  animals  with  the  herd.  The  method  of  keep- 
ing hogs  in  separate  houses  instead  of  in  a  large  hog^ 
house  has  much  to  recommend  it,  for  if  cholera  breaks  out 
in  one  part  of  the  herd,  it  can  often  be  kept  from  spread- 
ing to  the  other  sections  of  the  herd. 

Hogs  frequently  acquire  the  disease  from  infected 
cars,  shipping  crates,  etc.  The  disease  may  be  spread 
from  herd  to  herd  by  infected  objects,  such  as  farm  tools 
carried  from  one  farm  to  another.  The  farmer  himself 
may  inadvertantly  serve  to  disseminate  contagion,  by 
visiting  his  neighbor  to  inspect  an  infected  herd  and 
bringing  home  the  v virus  of  the  disease  in  the  slight 
amount  of  manure  that  may  cling  to  his  shoes.  Birds 
and  rats  may  also  carry  the  disease.  The  exhibition  of 
hogs  at  fairs  is  often  a  means  of  bringing  the  animals  in 
contact  with  the  disease. 

"When  hog  cholera  is  present  in  the  neighborhood,  the 
greatest  care  must  be  taken  to  prevent  its  introduction 
onto  the  farm.  At  the  first  signs  of  sickness  in  the  herd, 
all  animals  that  appear  healthy  should  be  removed  to  an- 
other field.  All  carcasses  of  hogs  that  have  died  of 
cholera  should  be  burned  or  buried  very  deeply,  first  cov- 


Diseases  of  Hogs.  155- 

ering  the  body  with  quick-lime.  Carcasses  should  never 
be  thrown  intd  streams  or  left  uncovered  to  decompose. 
The  pens  and  yards  should  be  thoroughly  cleaned  and 
well  sprinkled  with  quick  lime.  The  litter  and  manure 
should  be  burned.  After  a  lapse  of  several  months  the 
pens  should  be  whitewashed.  The  organism  does  not 
form  spores,  hence  is  easily  killed. 

Vaccination  and  serum  treatment.  For  many  years 
efforts  have  been  made  to  discover  a  vaccine  that  would 
protect  from  hog  cholera  as  the  black  leg  vaccine  pro- 
tects against  that  disease,  but  the  efforts  have  met  with 
little  success.  Eecently  methods  have  been  devised  that 
seem  to  promise  success  in  preventing  the  spread  of  the 
disease.  A  hog  that  has  recovered  from  an  attack  of  hog 
cholera  is  immune  to  further  attacks.  If  this  immune 
animal  is  inoculated  with  the  blood  of  animal  that  has 
the  disease,  the  amount  of  protective  substance  in  the 
blood  of  the  immune  animal  will  be  greatly  increased, 
so  much  so,  that  if  some  of  its  blood  serum  is  transferred 
to  a  second  animal,  it  will  be  protected  against  a  natural 
attack  of  the  disease  for  about  a  month.  This  method  of 
prevention  is  similar  to  the  use  of  antitoxin  in  lockjaw. 
If  it  is  desired  to  make  the  protection  more  permanent, 
a  small  amount  of  blood  from  a  diseased  hog  is  injected 
into  the  animal  at  the  same  time  the  serum  is  adminis- 
tered. In  this  case  the  protection  lasts  for  a  long  time, 
possibly  during  the  life  of  the  animal.  Many  difficulties 
are  encountered  in  the  use  of  the  serum  treatment  in  a 
practical  way.  It  is  to  be  hoped  that  these  may  be  over- 
come and  the  method  made  a  real  success.  The  treat- 
ment can  only  be  administered  by  a  trained  veterinarian, 
especially  is  this  true  when  the  virulent  blood  is  used  to- 
gether with  the  serum. 


156  Agricultural  Bacteriology. 

Swine  plague.  It  is  believed  that  swine  plague  is  a 
distinct  disease  from  hog  cholera,  produced  by  a  different 
organism.  The  diseases  often  occur  together,  each  pro- 
ducing its  peculiar  lesions  in  the  body  of  the  animal. 
From  the  standpoint  of  prevention,  all  that  has  been 
said  concerning  hog  cholera  applies  to  swine  plague.  It 
is  not  certain  whether  the  method  of  vaccination  against 
hog  cholera  is  of  any  value  in  cases  of  swine  plague.  It 
is  claimed  by  some  that  there  is  but  one  disease  caused 
by  an  organism  so  small  that  it  cannot  be  seen  with  the 
most  powerful  microscope,  and  that  the  organisms  sup- 
posed to  be  the  cause  of  hog  cholera  and  swine  plague  are 
of  secondary  importance.  Others  claim  that  there  are 
three  distinct  diseases. 

The  disease  of  swine  plague  is  primarily  one  of  the 
lungs  and  it  is  supposed  that  the  infection  occurs  through 
the  lungs.  The  lungs  may  show  consolidated  areas,  in 
which  the  organ  has  the  appearance  of  solid  flesh  or  liver, 
instead  of  the  spongy  normal  texture,  and  the  air  pas- 
sages may  be  filled  with  an  exudate. 


CHAPTER  XVI. 
DISEASES  OF  FOWLS. 

There  are  a  number  of  diseases  of  chickens  and  other 
fowls  caused  by  bacteria.  These  diseases  inflict  a  heavy 
tax  on  the  poultry  raiser  and  the  general  farmer.  Pres- 
ent knowledge  concerning  these  various  diseases  is  far 
from  complete ;  in  some  cases  not  sufficient  to  control  the 
disease  with  much  hope  for  success. 

Chicken  cholera.  Chickens  like  swine  are  subject  to 
dietary  disorders  which  may  often  simulate  a  true  con- 
tagious disease  in  the  rapidity  of  its  appearance  and  in 
the  high  mortality.  It  is  certain  that  most  of  the  out- 
breaks reported  as  chicken  cholera  are  not  caused  by  the 
specific  organism  of  chicken  cholera. 

Symptoms.  The  yellow  color  of  the  urates  is  the 
earliest  symptom ;  these  in  healthy  birds  are  pure  white. 
Diarrhea  is  present,  the  manure  varies,  sometimes  being 
a  pasty,  greenish  mass,  a  brownish-red  slimy  material  or 
a  thick  clear  liquid.  The  sick  bird  leaves  the  flock,  be- 
comes weak  and  drowsy,  acts  dumpish,  and  the  feathers 
are  roughened.  Intense  thirst  is  usually  noticed,  the  ap- 
petite is  poor  and  the  crop  distended  with  food.  The 
diseased  fowls  rapidly  become  poor.  The  disease  makes 
rapid  headway  in  the  flock  since  the  period  of  incubation 
is  short,  (one  to  three  days.)  Most  of  the  affected  birds 
die  in  a  short  time  of  an  acute  form  of  the  disease;, 
others  may  have  the  chronic  form,  but  recovery  is  rare. 


158  Agricultural  Bacteriology. 

Post-mortem  examination.  The  liver  is  usually  very 
much  enlarged  and  softened;  the  intestinal  organs  are 
congested,  but  the  changes  are  not  such  as  make  it  easy 
to  diagnose  the  disease. 

Manner  of  infection.  The  bacteria  are  found  in  the 
blood  at  the  time  of  death.  If  any  part  of  the  carcass 
is  consumed  by  well  birds,  they  are  certain  to  become  in- 
fected. The  only  known  manner  of  infection  is  by  the 
food  or  water.  The  material  that  drops  from  the  beak 
of  the  sick  fowl  may  serve  to  contaminate  the  drinking 
water.  The  extensive  lesions  of  the  intestines  allow 
blood  to  be  mixed  with  the  manure,  and  the  contamina- 
tion of  the  food  with  this  material  is  a  cause  of  rapid 
spread  of  the  trouble. 

The  disease  may  begin  in  a  flock  by  the  introduction 
of  a  bird  ill  with  the  chronic  type  of  the  disease.  Doves 
and  wild  birds  are  also  supposed  to  be  agents  concerned 
in  the  spread  of  cholera.  The  improper  disposal  of  dead 
birds,  as  by  throwing  them  into  a  stream  may  cause  in- 
fection of  flocks  at  a  distance. 

Prevention.  Nothing  can  be  done  for  the  already  in- 
fected bird.  All  efforts  must  be  concentrated  in  pre- 
venting the  spread  of  the  trouble,  by  the  prompt  dis- 
posal of  all  dead  birds,  the  killing  of  any  that  show 
signs  of  illness,  thorough  disinfection  of  the  roosting 
houses,  and  the  feeding  and  watering  troughs.  If  pos- 
sible the  flock  should  be  moved  onto  fresh,  uncontamin- 
ated  grounds.  The  germ  is  easily  killed  by  drying,  sun- 
light, and  disinfectants.  It  has  been  shown  by  experi- 
ment that  it  is  safe  to  bring  new  stock  onto  land  after  a 
period  of  two  weeks,  if  care  has  been  taken  in  the  disin- 
fection of  the  house  and  other  contaminated  objects. 


Diseases  of  Fowls.  159 

Fowl  typhoid.  This  disease  is  thought  to  be  more 
widely  spread  than  chicken  cholera.  The  disease  is  less 
rapid  in  its  progress  in  the  individual  bird,  than  is 
cholera.  It  is  often  mistaken  for  this  disease  for  there 
are  no  marked  differences  in  the  symptoms.  The  diar- 
rhea so  characteristic  of  cholera  is  usually  absent  and  the 
intestines  are  pale  instead  of  deep  red,  and  the  contents 
of  normal  consistency,  while  in  cholera  the  intestinal  con- 
tents are  liquid  and  blood  stained.  It  is  not  especially 
important  that  a  correct  diagnosis  be  made  as  to  which 
of  these  diseases  is  present  in  the  flock,  since  identical 
methods  of  prevention  should  be  employed  with  either. 

Roup,  or  diphtheria  in  fowls.  The  disease  of  diph- 
theria of  fowls  is  not  caused  by  the  same  organism  caus- 
ing diphtheria  in  human  beings.  It  is  considered  to  be 
the  most  important  disease  of  chickens  in  this  country. 
It  is  claimed  that  it  affects  turkeys,  ducks,  pigeons,  and 
pheasants,  as  well  as  chickens.  The  cause  of  roup  has 
not  been  discovered  with  certainty. 

The  first  symptom  to  be  noted  is  a  discharge  of  a  wat- 
ery liquid  from  the  nostrils,  and  often  from  the  eyes, 
and  the  bird  becomes  dumpish.  The  breathing  is  often 
noisy,  due  to  the  obstruction  of  the  air  passages  with  the 
discharge ;  the  fowl  may  be  able  to  breathe  only  by  open- 
ing its  mouth.  Sneezing  is  frequent.  Diarrhea  appears 
later,  the  evacuations  being  greenish  or  yellowish.  The 
eyes  may  be  covered  with  the  dried  discharge,  or  they 
may  be  forced  from  their  sockets,  due  to  the  accumula- 
tion of  cheesy  matter  in  the  sockets.  There  are  to  be 
found  in  the  mouth  and  throat,  patches  of  grayish-yellow 
exudations,  called  false  membranes  which  are  similar  to 
the  membranes  formed  in  the  case  of  diphtheria  in  human 
beings.  The  closing  of  the  throat  by  the  membrane 


160  Agricultural  Bacteriology. 

causes  death  by  suffocation.  The  accumulation  of  the 
exudate  in  the  cavities  of  the  head  often  causes  a  swelling, 
hence  the  common  name  for  the  disease  "swell-head." 

The  disease  is  to  be  differentiated  from  simple  catarrhr 
which  closely  resembles  the  "cold  in  the  head"  of  man. 
Simple  catarrh  is  caused  by  improper  ventilation  of 
houses,  dampness,  cold  winds,  and  exposure.  Roup  is 
often  supposed  to  be  produced  by  similar  conditions.  It 
has  been  shown  experimentally  that  it  is  not  possible  to 
produce  it  by  such  means,  although  they  undoubtedly 
favor  its  spread  when  once  it  is  started  in  the  flock. 

Prevention  and  treatment.  The  disease  is  most  often 
introduced  into  the  flock  by  the  purchase  of  a  bird  having 
the  disease  in  such  a  mild  form  that  no  symptoms  are 
noticeable.  Fowls  that  come  from  flocks  in  which  the 
disease  is  present  or  has  been  recently  present  should  not 
be  placed  with  other  flocks.  Any  bird  showing  an  ex- 
udate from  the  nostrils  or  eyes  should  be  removed  from 
the  flock  at  once.  Care  should  be  taken  to  avoid  distri- 
bution of  infection  from  diseased  flocks  to  healthy  ones, 
by  means  of  the  dirt  on  boots,  farm  implements,  etc. 

The  dipping  of  the  heads  of  the  affected  birds  in  a  2 
per  cent  solution  of  .potassium  permanganate  is  said  to  be- 
an aid  in  the  treatment  of  the  disease. 


CHAPTER  XVII. 
MISCELLANEOUS  DISEASES. 

Diseases  caused  by  wound  infection.  There  are 
many  diseases  of  domestic  animals  that  are  produced  by 
organisms  that  enter  the  body  through  wounds.  One  of 
the  most  important  is  that  known  as  white  scours  or  diar- 
rhea in  calves.  It  affects  calves  a  few  hours  to  a  few 
days  old,  causing  death  in  70  to  90  per  cent  of  cases. 
The  discharges  from  the  bowels  are  light  colored,  profuse 
and  very  offensive  in  odor.  The  animals  lose  flesh 
rapidly  and  have  the  appearance  of  suffering  from  severe 
sickness.  The  duration  of  the  disease  is  from  three  to 
six  days.  It  rarely  attacks  calves  after  they  are  from 
two  to  three  days  old.  Once  established  in  a  stable,  the 
disease  may  persist  for  years  unless  stringent  means  are 
taken  to  rid  the  stable  of  the  infection. 

Treatment  is  of  no  value.  Attention  must  be  directed 
to  prevention.  It  is  believed  that  the  organisms  enter 
the  body  through  the  umbilical  cord  and  that,  if  means 
are  taken  to  prevent  such  infection,  no  trouble  will  re- 
sult. In  order  to  accomplish  this,  the  animal  about  to 
calve  should  be  placed  in  a  clean  stall  with  an  abundance 
of  bedding.  The  tail,  hips,  and  external  genital  parts 
should  be  sponged  with  a  solution  of  carbolic  acid  or  cor- 
rosive sublimate  (1-2500).  The  cord  of  the  young  ani- 
mal should  be  cleaned  carefully  and  a  mixture  of  one 
ounce  of  tincture  of  iodine  in  two  ounces  of  glycerine  ap- 
plied. The  treatment  is  to  be  repeated  daily  for  three 


162  Agricultural  Bacteriology. 

or  four  days.  The  stable  should  be  disinfected  and  all 
infectious  matter  destroyed. 

The  infection  of  the  umbilical  cord  in  colts  and  lambs 
may  serve  to  produce  a  general  infection  of  the  body 
with  harmful  organisms.  Infection  of  the  spermatic 
cord  in  the  castration  of  colts  often  produces  serious 
troubles.  All  minor  surgical  operations  on  animals 
should  be  carried  out  with  regard  to  cleanliness  of  the 
part  to  be  operated  upon,  the  hands  of  the  operator  and 
his  instruments. 

It  is  also  generally  believed  that  two  very  common 
troubles  in  the  horse,  fistulous  withers  and  poll  evil,  are 
due  to  wound  infection  with  pus-forming  bacteria.  The 
wound  need  not  be  a  noticeable  one,  an  irritation  of  the 
skin  due  to  ill  fitting  harness,  saddles  or  blows  being  suf- 
ficient to  introduce  the  organisms  found  in  the  skin  into 
the  deeper  tissues  where  growth  is  possible. 

Foot-rot  in  sheep  is  due,  at  least  in  many  cases,  to  the 
infection  of  the  tissues  of  the  foot  with  pus-producing 
bacteria.  The  disease  may  pass  from  one  animal  to  an- 
other until  a  large  part  of  the  flock  is  infected.  The 
local  application  of  disinfectants  is  the  treatment  em- 
ployed. 

Foot  and  mouth  disease.  Foot  and  mouth  disease  is 
one  of  the  important  diseases  of  Europe.  It  affects 
cattle,  swine,  and  also  man.  From  Europe  it  has  been 
exported  to  other  countries,  especially  to  America.  In 
1870  it  was  present  in  New  England  and  New  York.  In 
1884  an  outbreak  occurred  at  Portland,  Maine.  In  1902 
the  disease  was  introduced  into  Massachusetts,  New 
Hampshire,  Vermont,  Ehode  Island;  in  1908  in  New 
York,  Pennsylvania  and  Michigan.  By  prompt  action, 
the  disease  was  stamped  out  at  each  of  these  outbreaks. 


Miscellaneous  Diseases.  163 

The  disease  is  marked  by  the  appearance  of  blisters  on 
the  lips,  gums,  tongue,  and  inside  of  the  cheeks.  One  or 
more  feet  may  be  diseased.  Blisters  appear  on  the  coro- 
net and  between  the  hoofs  and  often  on  the  teats.  Re- 
covery is  usual  except  in  very  young  animals. 

One  important  phase  of  the  disease  is  that  the  organ- 
isms, whose  nature  is  unknown,  are  often  present  in  the 
milk.  People  using  such  milk  in  a  raw  form  are  thereby 
infected.  The  disease  in  man  presents  much  the  same 
symptoms  as  in  the  cow.  Hogs  also  acquire  the  disease 
from  milk. 

Distemper  in  horses.  Influenza,  or  as  it  is  frequently 
called  distemper  or  pink  eye,  is  a  contagious  disease,  the 
cause  of  which  is  unknown.  Infection  takes  place  from 
horse  to  horse.  The  virus  can  be  carried  by  infected 
human  beings,  litter  and  harness,  etc.  The  period  of  in- 
cubation is  two  to  seven  days.  The  disease  appears 
quickly.  It  is  marked  by  a  loss  of  appetite,  a  fever  of 
3°  to  4°  F.  above  normal,  persisting  for  three  to  six  days. 
The  animal  is  dull;  at  first  it  is  constipated;  the  feces 
are  in  hard  balls,  covered  with  slimy  matter,  later  diar- 
rhea is  present.  The  eyes  are  inflamed.  The  disease 
lasts  six  to  ten  days.  From  2  to  4  per  cent  of  the  af- 
flicted animals  die. 

Distemper  in  dogs.  Distemper  is  the  most  important 
disease  of  dogs.  The  cause  is  not  known;  the  period  of 
incubation  is  four  to  six  days.  The  eyes  are  inflamed, 
the  exudate  dries  and  often  causes  the  lids  to  adhere  to 
each  other.  Constipation  at  first,  is  followed  by  diar- 
rhea in  which  the  feces  have  an  offensive  odor,  and  are 
often  slimy  and  frothy.  There  is  a  nasal  discharge.  It 


164  Agricultural  Bacteriology. 

may  affect  the  brain  and  the  animal  is  then  often  thought 
to  be  rabid.  The  mortality  ranges  from  50  to  60  per 
cent.  The  only  means  of  prevention  of  the  spread  of  the 
disease  is  by  isolation  of  all  diseased  animals,  and  the  use 
of  disinfectants. 


CHAPTER  XVIII. 
DISINFECTION. 

It  has  been  seen  that  the  disease-producing  bacteria 
pass  from  the  bodies  of  living  and  dead  animals  in  a 
number  of  ways,  as  in  the  material  coughed  up  from  the 
lungs,  as  in  tuberculosis ;  in  the  manure,  as  in  hog 
cholera;  in  the  milk,  as  in  tuberculosis;  in  the  contents 
of  abscesses  and  carbuncles,  as  in  anthrax,  black  leg,  and 
pyogenic  troubles,  and  in  the  discharges  from  the  nostrils, 
as  in  glanders.  The  bacteria  thrown  off  from  the  bodies 
of  the  diseased  animal  contaminate  the  stables,  yards, 
and  fields,  and  from  these  contaminated  places  and  ob- 
jects often  enter  the  bodies  of  healthy  animals  thus  serv- 
ing to  perpetuate  the  disease  in  the  herd. 

If  the  farmer  is  to  stop  the  spread  of  transmissible  dis- 
ease, he  must  destroy  in  some  effective  way  the  bacteria 
that  have  been  thrown  off  from  the  bodies  of  diseased 
animals.  In  short  he  must  disinfect  the  barns  and 
stables,  and  as  far  as  is  possible  the  yards  and  fields. 

In  the  destruction  of  the  pathogenic  bacteria  consider- 
ation must  first  be  given  to  the  resistance  of  the  organism 
it  is  desired  to  destroy.  For  this  purpose  the  various 
disease-producing  bacteria  may  be  divided  into  two 
classes;  those  that  ^produce  spores  and  those  that  do  not 
form  these  resistent  bodies.  The  former  class  of  bac- 
teria are  very  difficult  to  kill,  the  latter  are  easily  de- 
stroyed. Fortunately,  but  two  of  the  important  dis- 
eases of  animals  are  produced  by  spore-bearing  bacteria. 


166  Agricultural  Bacteriology. 

black  leg  and  anthrax.  The  most  important  and  most 
common  of  the  diseases  affecting  the  domestic  animals 
are  caused  by  bacteria  that  do  not  form  spores. 

Disinfectants.  Disinfecting  agents  may  be  divided 
into  two  classes,  physical  and  chemical.  The  effect  of 
the  most  important  physical  disinfectant,  sunlight,  has 
been  discussed  in  a  previous  chapter.  Sunlight  rapidly 
destroys  all  vegetating  bacteria  and  their  spores  as  well, 
if  it  falls  directly  upon  them.  If,  however,  they  are  cov- 
ered with  a  layer  of  dirt  or  dust  even  though  it  be  very 
thin,  the  sunlight  has  little  effect  on  them.  Diffuse  light, 
such  as  is  present  where  the  direct  rays  of  the  sun  do  not 
penetrate,  is  very  weak  in  its  action,  requiring  hours  and 
days  to  produce  the  same  effect  as  a  few  moments  of  di- 
rect sunlight.  It  is  very  certain  that  sunlight  under  the 
conditions  that  obtain  in  barns  and  stables  has  but  little 
disinfecting  action,  because  of  the  fact  that  the  bacteria 
are  protected  from  its  action  by  the  dirt  and  dust. 

Another  physical  agent  of  which  little  use  can  be  made 
in  the  disinfection  of  stables  is  heat,  either  as  dry  heat  or 
in  the  form  of  steam  or  hot  water.  Any  small  object  of 
wood  or  iron  can  be  easily  disinfected  by  boiling.  Thus, 
in  the  case  of  contagibus  diseases  of  human  beings,  this 
process  is  frequently  used.  In  the  disinfection  of  stables 
etc.,  one  is  limited  to  the  use  of  chemicals. 

Chemical  disinfectants.  The  chemicals  used  for  dis- 
infection may  be  divided  into  two  classes,  solid  materials 
used  in  suspension  or  in  solution,  and  gaseous.  The  lat- 
ter are  by  far  the  best  when  the  conditions  will  permit  of 
tneir  use  for  the  gas  penetrates  to  every  part  of  the  space 
to  be  treated,  even  into  cracks  and  crevices.  This  fact 
makes  their  use  impossible  except  in  a  space  that  can  be 
tightly  closed,  for  the  gas  must  be  confined  for  several 


Disinfection.  167 

hours  in  the  space  to  be  disinfected  in  order  that  the  pro- 
cess shall  be  effective.  The  gaseous  disinfectants  find 
their  greatest  use  in  household  disinfection,  where  the 
rooms  can  be  tightly  closed  by  pasting  strips  of  paper 
over  the  door  and  window  cracks.  Formaldehyde,  the 
best  gaseous  disinfectant,  finds  but  limited  use  in  the 
stable.  Keliance  must  here  be  placed  on  the  disinfect- 
ants that  can  be  applied  in  solution  or  suspension  in 
water.  There  are  a  considerable  number  of  these  but 
three  or  four  are  by  far  the  most  important. 

Lime.  Quick  lime  or  stone  lime  is  made  by  heating 
lime  stone  to  a  very  high  temperature.  The  lime  stone 
is  changed  because  of  the  loss  of  carbon  dioxide,  which 
passes  off  as  a  gas  during  the  burning  of  the  lime  stone. 
The  quick  lime  thus  produced  gradually  changes  on  ex- 
posure, to  a  powder  known  as  air-slaked  lime  which  has 
the  same  composition  as  the  original  lime  stone,  and  which 
has  no  disinfecting  action  whatever.  If  the  quick  lime  is: 
treated  with  six  parts  of  water  to  ten  parts  of  lime, 
water-slaked  lime  will  be  obtained,  which,  when  prepared 
in  a  cornet  manner,  is  a  dry  white  powder,  resembling 
air-slaked  lime  in  appearance  but  not  in  composition. 
This  can  be  noted  by  placing  a  particle  of  each  on  the 
tongue  for  a  moment.  The  air-slaked  lime  tastes  like  so- 
much  chalk  while  the  water-slaked  soon  causes  the  tongue 
to  burn.  It  is  caustic  lime  and  has  disinfecting  proper- 
ties. It  can  be  used  as  a  dry  powder,  sprinkled  on  floors 
and  yards,  or  in  a  suspension,  in  water  as  whitewash. 
The  whitewash  is  best  applied  with  a  spray  pump  and  for 
this  purpose  must  be  made  rather  thin  so  as  not  to  clog 
the  nozzle  of  the  pump.  Any  of  the  hand  spraying  out- 
fits are  well  adapted  for  the  application  of  whitewash  or 
other  disinfectants  to  the  walls  and  ceilings  of  stables. 


168  Agricultural  Bacteriology. 

Lime  is  cheap,  and  can  be  procured  everywhere.  If 
the  whitewash  is  prepared  from  good  lime,  its  disinfect- 
ing properties  are  probably  as  great  as  those  of  any  other 
substance  that  can  be  used  to  advantage  in  stable  disin- 
fection. It  has,  however,  little  effect  on  spores  of  bac- 
teria. The  whitewashed  walls  and  ceilings  make  the 
stable  much  lighter  than  would  otherwise  be  the  case. 
The  dry  water-slaked  lime  is  especially  valuable  for  the 
treatment  of  yards  and  pens  infected  with  hog  cholera 
bacilli  and  for  covering  the  carcasses  of  all  animals  that 
have  died  of  any  of  the  transmissible  diseases,  and  which 
are  to  be  buried. 

Carbolic  acid  and  cresol  compounds.  Carbolic  acid 
appears  on  the  market  in  the  crude  and  purified  forms. 
The  former  is  a  black,  oily  liquid  that  will  not  mix  with 
water,  unless  treated  with  strong  acids,  such  as  sulphuric 
acid,  or  with  strong  alkalies.  The  pure  carbolic  acid  is 
in  the  form  of  white  crystals,  which  on  the  addition  of  5 
per  cent  of  water,  and  on  warming,  changes  to  a  clear 
liquid  of  the  consistency  of  syrup.  For  use  as  a  general 
disinfectant,  this  liquid  is  added  to  water  so  a»to  make 
a  5  per  cent  solution.  A  stronger  solution  than  this  will 
not  dissolve  in  water/ 

Both  the  crude  and  purified  carbolic  acid  are  being  re- 
placed for  disinfection  purposes  by  the  different  proprie- 
tary compounds  such  as  ZenoLeum,  Kresol,  etc.  These 
substances  have,  as  a  rule,  greater  disinfecting  powers 
than  carbolic  acid,  a  2  per  cent  solution  being  as  effective 
as  a  5  per  cent  solution  of  carbolic  acid.  They  mix  with 
water  in  all  proportions,  forming  a  milky  white  emulsion 
that  can  be  easily  applied  with  a  brush  or  spray  pump. 
They  are  less  caustic  and  poisonous  than  carbolic  acid, 
but  their  cost  is  somewhat  more. 


D/sinfcction.  169 

Corrosive  sublimate.  This  compound,  frequently 
called  bichloride  of  mercury,  is  the  strongest  disinfectant 
known.  Its  great  disadvantage  as  a  stable  disinfectant 
is  its  poisonous  properties,  which  preclude  its  use  on 
mangers.  It  is  used  in  a  one  to  one  thousand  solution,  one 
ounce  in  eight  gallons  of  water.  It  kills  all  forms  of  bac- 
teria in  a  moment  and  the  spores  in  a  short  time  when  no 
substance  is  present  that  will  combine  with  it  and  thus 
destroy  its  action  on  the  bacteria.  In  the  presence  of 
dirt  and  manure  its  effect  is  greatly  reduced. 

Ferrous  sulphate  and  copper  sulphate.  These  sub- 
stances known  as  green  and  blue  vitriol,  respectively, 
were  formerly  considered  to  be  good  disinfectants.  It  is 
now  known  that  they  are  almost  worthless  in  this  re- 
spect. They  are  rather  to  be  classed  as  deodorants,  and 
can  often  be  used  for  this  purpose  to  good  advantage.  A 
substance  that  will  counteract  the  odors  produced  by 
bacteria  does  not  necessarily  destroy  the  bacteria  them- 
selves. 

Formaldehyde.  This  disinfectant  is  sold  as  a  solu- 
tion of  the  gas,  formalin,  in  water.  It  can  be  applied 
as  a  5  per  cent  solution,  but  since  the  gas  at  once  passes 
off,  it  has  but  little  value  as  a  stable  disinfectant.  Small 
objects,  other  than  those  of  leather,  to  be  disinfected  can 
be  placed  in  a  solution  of  formaldehyde. 

The  process  of  stable  disinfection.  Whenever  a  sta- 
ble is  to  be  disinfected,  the  first  process  should  be  to  give 
it  a  thorough  cleaning.  It  should  be  remembered  that 
no  disinfectant  can  kill  a  disease-producing  organism 
with  which  it  does  not  actually  come  in  contact.  If  the 
organism  is  protected  by  dust,  dirt,  and  dried  manure, 
its  destruction  is  difficult.  The  most  of  the  disease-pro- 


170  Agricultural  Bacteriology. 

ducing  germs  will  be  in  the  dirt  and  manure  of  the  stable. 
If  the  stable  is  thorough^  cleaned  most  of  the  bacteria 
will  have  been  removed. 

All  loose  woodwork,  especially  box  mangers,  should  be 
removed.  The  walls,  ceilings,  and  floors  should  be  mois- 
tened by  spraying  with  a  solution  of  corrosive  sublimate 
so  as  to  prevent  dust  in  the  subsequent  operations.  The 
loose  material  should  all  be  removed ;  the  walls  and  floors 
scraped  until  all  dried  manure  and  dirt  is  removed  and 
the  bare  wood  or  concrete  exposed.  All  the  material  re- 
moved should  be  burned,  not  thrown  into  the  yard  with 
the  cattle.  The  stable  should  now  receive  a  good  coat  of 
whitewash  applied  with  a  spray  pump  so  .that  it  will 
penetrate  all  cracks.  Both  walls  and  ceilings  should  be 
treated,  and  the  floors  sprinkled  with  the  dry  water-slaked 
lime.  The  mangers  should  be,  scrubbed  with  a  hot  solu- 
tion of  lye,  or  a  5  per  cent  solution  of  carbolic  acid.  The 
actual  process  of  disinfection  should  be  supplemented  by 
making  provision  for  abundant ,  light  and  air.  A  half- 
hearted job  of  disinfection  is  worse  than  none  at  all,  since 
it  gives  a  fancied  security,  but  little  real  security  against 
a  re-occurrence  of  the  disease. 

The  disinfection  of  x  yards  is  difficult.  It  can  only  be 
attempted.  The  sprinkling  of  a  liberal  amount  of  dry 
water-slaked  lime  is  the  best  that  can  be  done.  The  dis- 
infection of  fields  is  impossible.  Small  areas  may  be 
limed  or  burned  over.  Neither  of  these  methods  is  likely 
to  be  effective  in  the  case  of  spore-forming  bactria.  All 
other  forms  will  soon  die  without  the  addition  of  any 
disinfectant. 


SECTION  IV. 
RELATION  OF  BACTERIA  TO  SOIL. 


CHAPTER  XIX. 
RELATION  OF  BACTERIA  TO  FERTILITY. 

The  farmer  is  interested  in  the  soil  as  the  home  of  the 
plant.  Unless  its  home  is  one  favorable  in  every  way  to 
the  kind  of  plants  the  farmer  is  attempting  to  grow  but 
meager  yields  will  reward  his  efforts.  In  order  that  the 
soil  shall  be  a  favorable  place  for  such  growth,  a  num- 
ber of  conditions  must  be  present.  Its  physical  proper- 
ties are  important.  It  must  not  be  hard  and  dense  so 
that  the  delicate  roots  of  the  young  plant  in  search  of 
food  cannot  make  their  way  through  it.  It  must  be  in 
good  tilth.  Moisture,  not  too  abundant  or  too  small  in 
amount,  must  be  available.  The  temperature  of  the  soil 
must  be  conducive  to  rapid  plant  growth.  These  things 
are  all  important  and  are  to  a  great  extent  at  least  under 
the  control  of  the  farmer. 

•  Plant  food.  Another  important  condition  required 
is  the  presence  of  a  sufficient  supply  of  plant  food  in  an 
available  form  f or  4ise  by  the  plant.  Certain  chemical 
elements  as  potassium,  calcium,  magnesium,  phosphorus, 
nitrogen,  sulphur,  and  iron  are  essential  in  order  that 
normal  development  may  occur.  These  substances  the 
plant  obtains  from  the  soil.  The  carbon,  oxygen,  and 


172  Agricultural  Bacteriology. 

hydrogen  which  are  as  essential  as  the  other  chemical 
elements  mentioned  are  always  abundantly  present  in  an 
available  form  in  the  water  and  in  the  air. 

The  elements  obtainable  from  the  soil  are  a  greater 
source  of  worry. to  the  farmer.  While  the  soil,  as  a  rule, 
contains  large  amounts  of  these  different  elements,  they 
may  be  present  in  such  forms  that  they  cannot  be  utilized 
by  the  green  plant.  "While  they  represent  plant  food, 
it  is  of  no  immediate  value  because  unavailable.  This 
material  is,  however,  undergoing  a  change  in  form  that 
renders  it  more  and  more  available.  A  large  number  of 
agencies  are  at  work,  causing  this  change  and  amongst 
them  biological  factors  are  very  important. 

As  indicating  the  relatively  large  amount  of  unavail- 
able plant  food  that  may  be  present,  the  following  analy- 
sis of  49  American  soils  are  presented.  The  total  nitro- 
gen, phosphorus  and  potash  content  of  the  first  eight 
inches  was  as  follows :  2600  pounds  of  nitrogen  per  acre, 
2090  pounds  of  phosphorus,  and  7400  pounds  of  potas- 
sium. The  other  essential  elements  are  usually  present 
in  larger  amounts  and  therefore  are  not  so  likety  to  be 
depleted  in  the  soil  as  are  the  three  mentioned. 

The  amount  of  any  of  these  elements  that  are  available 
at  any  one  time  is  usually  very  small  indeed.  Often,  it 
is  not  enough  to  furnish  what  is  needed  for  a  single  crop. 
The  potential  but  immediately  unavailable  supply  must 
be  constantly  changed  into  available  food  at  a  rate  suffi: 
ciently  rapid  to  supply  the  plant  so  that  growth  may  go 
on  rapidly  or  otherwise  the  crop  will  be  a  poor  one.  A 
fertile  soil  may,  in  one  sense,  be  defined  as  one  in  which 
unavailable  plant  food  is  being  changed  to  available  food 
at  such  a  rate  that  there  is  an  abundant  supply  at  all 


Relation  of  Bacteria  to  Fertility.  173 

times  to  allow  of  a  rapid  and  luxuriant  growth  of  the 
plants. 

The  food  to  be  available  to  the  plant  must  be  in  solu- 
tion so  that  it  can  pass  into  the  roots  of  the  plant.  Such 
soluble  material  is  easily  lost  in  the  drainage  water  that 
leaches  from  the  soil  during  the  wet  times  of  the  year. 
Thus,  if  more  of  any  one  element  is  made  available  than 
the  crop  can  use,  it  is  very  likely  to  be  lost  during  the 
winter  and  spring,  and  the  soil  thus  robbed  of  its  fer- 
tility. An  ideal  condition  is  to  have  enough  of  each  ele- 
ment rendered  available  so  as  to  ensure  an  abundant 
crop,  but  not  to  have  an  excess.  This  ideal  condition 
cannot  be  realized  but  much  can  be  done  by  the  farmer 
to  conserve  the  fertility  of  his  soil  by  methods  which  will 
be  mentioned  later. 

If  any  one  of  the  essential  elements  is  lacking,  or  is 
present  only  in  small  amounts  in  available  form,  it  will 
act  as  a  limiting  factor  to  the  yield.  One  element  is  as 
essential  as  another.  Any  may  be  the  limiting  one.  If 
this  be  added  to  the  soil  in  the  form  of  a  fertilizer,  an 
immediate  increase  in  yield  is  noted.  For  this  reason  the 
use  of  commercial  fertilizers  is  so  extensive.  The  fer- 
tility can  also  be  restored  by  treating  the  soil  in  such  a 
way  as  to  render  the  unavailable  plant  food  available. 
For  example,  it  ;has  been  shown  in  certain  of  the  wheat 
fields  of  the  Rothamsted  Experiment  Station  in  England 
that  the  amount  of  available  phosphorous  present  in  the 
soil  was  so  small  as  to  limit  the  yield,  yet  this  same  soil 
contained  a  large  amount  of  the  element  in  an  insoluble 
form.  By  treating  the  soil  in  a  proper  manner  so  as  to 
allow  the  growth  of  certain  kinds  of  bacteria,  the  phos- 
phorus would  be  made  soluble  and  the  fertility  of  the 
soil  improved. 


174  Agricultural  Bacteriology. 

The  same  is  true  with  reference  to  the  other  essential 
-elements.  It  thus  becomes  important  to  know  something 
concerning  the.  conditions  that  are  favorable  for  the 
growth  of  the  bacteria  in  the  soil.  The  yield  of  the  vis- 
ible crop  is  dependent  on  the  way  in  which  the  farmer 
favors  the  growth  of  the  invisible  crop.  This  presents 
a  new  phase  of  soil  management  which  has  not  long  been 
recognized,  as  the  soil  has  generally  been  regarded  as  an 
inert  mass  of  particles  of  sand,  clay,  or  gravel,  inter- 
mixed with  more  or  less  dead  organic  matter  which  gave 
to  the  upper  portion  its  black  color. 

Since  there  is  no  store  of  available  plant  food  in  the 
soil  and  since  the  bacteria  are  necessary  in  order  to 
change  the  raw  food  to  a  fitting  form,  it  is  evident  that 
a  soil  that  is  free  from  bacteria  cannot  be  a  fertile  one. 
If  various  types  of  soils  are  examined  as  to  the  number 
of  bacteria,  it  will  be  found  that  those  of  high  fertility 
are  teeming  with  bacteria  while  a  poor  sandy  soil  will 
contain  very  few. 

Distribution  of  bacteria  in  the  soil.  The  soil  is  one 
of  the  great  homes  of  the  bacteria.  In  a  state  of  nature, 
i.  e.,  in  uncultivated  soil,  everything  that  the  soil  yields 
is  returned  to  it,  either  directly  in  the  i  form  of  the  dead 
plant,  or  indirectly  in  the  body  or  excreta  of  an  animal 
that  has  lived  on  the  plants.  This  means  that  organic 
matter  in  abundance  is  supplied  as  food  to  the  bacteria; 
hence  their  rapid  increase  in  numbers  where  requisite 
conditions  obtain.  This  activity  renders  still  more  raw 
plant  food  available  with  the  result  that  the  soil  con- 
tinues to  increase  in  fertility  until  there  have  been 
formed  from  the  bare  rock  by  the  aid  of  various  physi- 
cal agencies  that  help  in  disintegrating  the  rock  such 
fertile  soils  as  are  found  on  our  western  prairies. 


Relation  of  Bacteria  to  Fertility.  175 

It  is  impossible  to  determine  in  any  way  the  total 
number  of  bacteria  in  the  soil.  What  can  be  done  is  to 
determine  the  number  that  will  grow  on  such  substances 
as  are  used  in  the  laboratory  as  culture  media.  Exam- 
ined in  this  way  a  sandy  soil  will  be  found  to  contain  a 
few  hundred  thousands  in  each  gram  (1-30  of  an  ounce) 
while  a  rich  loamy  soil  may  contain  several  million  per 
gram.  A  garden  soil  may  show  ten,  twenty-five,  or  even 
fifty  millions  of  these  minute  plants  so  essential  to  the 
fertility  of  the  soil.  The  greatest  number  of  bacteria  is 
found  in  the  first  few  inches  of  the  soil,  in  what  is  known 
as  the  soil  proper.  In  the  sub-soil  smaller  numbers  are 
found  and  as  still  lower  depths  are  examined  the  bac- 
teria decrease  rapidly  in  numbers.  At  a  depth  of  a  few 
feet  they  completely  disappear.  The  reason  for  this 
rapid  decrease  in  numbers  is  due  to  the  lack  of  food  and 
air,  and  to  the  filtering  effect  of  the  soil.  In  the  upper 
layers  of  the  soil  food  is  abundant  and  other  growth  con- 
ditions favorable. 

The  soil  contains  a  large  number  of  different  kinds  of 
bacteria  of  the  most  varied  nature  and  appearance.  It 
is  the  home  of  some  of  those  that  produce  diseases  in  man 
and  animals,  as  well  as  the  most  of  those  forms  that  cause 
the  spoiling  of  food  substances,  and  the  various  fermen- 
tations, many  of  which  are  so  important.  The  number 
of  bacteria  in  the  soil  is  influenced  by  a  number  of  fac- 
tors, chief  of  which  is  the  amount  of  food  present.  The 
addition  of  organic  matter  in  the  form  of  stable  manure, 
or  plowing  under  a  green  crop,  increases  the  amount  of 
food  material,  thus  stimulating  the  growth  of  bacteria. 

The  effect  of  temperature  is  also  of  importance.  As 
the  soil  becomes  warm  in  the  spring,  the  conditions  be- 
come more  favorable  and  the  bacteria  increase  rapidly  in 


376  .  Agricultural  Bactenoiogy. 

numbers.  The  rise  in  temperature  has  more  effect  at 
this  time  of  the  year  than  later,  since  the  supply  of  avail- 
able food  is  likely  to  be  greater  than  during  the  summer 
an.'l  fall,  due  to  the  fact  that  the  remains  of  the  previous 
crop  are  added  to  the  soil. 

The  moisture  content  also  exerts  an  influence.  Bac- 
teria demand  a  considerable  amount  of  water  for  their 
growth.  If  the  soil  is  very  dry,  cell  development  is  slow 
or  ceases.  Again,  if  the  soil  is  water  logged  as  in 
marshes  and  low  lands,  the  growth  of  certain  essential 
kinds  of  bacteria  is  impossible,  due  to  the  fact  that  they 
cannot  get  a  supply  of  oxygen.  Such  wet  soils  warm  up 
very  slowty  and  this  acts  as  a  restraining  factor  in  bac- 
terial growth.  If  the  low  places  are  drained,  the  ex- 
cess of  water  is  removed  and  air  is  allowed  to  penetrate 
the  soil  and  bacterial  action  is  more  rapid,  both  because 
of  increased  aeration  and  higher  temperature.  The 
effect  of  an  abundant  supply  of  oxygen  is  to  increase  the 
growth  of  the  most  important  classes  of  soil  bacteria  as 
is  noted  in  soils  thoroughly  cultivated.  Permanent  pas- 
ture and  woodland  soils  are  poorly  aerated  and  in  them 
certain  kinds  of  bacteria  grow  poorly.  As  a  result  these 
lands  never  produce  such  large  amounts  of  plant  growth 
each  year  as  does  the  same  soil  under  cultivation. 

The  bacteria  as  a  rule  grow  best  in  an  alkaline  medium, 
and  this  is  especially  true  of  many  soil  bacteria.  The 
soils  of  marshes  and  lowlands  in  general  is  apt  to  be  acid 
in  reaction.  Soils  that  have  been  cultivated  for  long* 
periods  without  having  had  returned  to  them  organic 
matter,  barnyard  or  green  manures,  tend  to  become  acid. 
In  such  soils  the  bacteria  cannot  grow  well.  If  the  acid- 
ity is  neutralized  by  the  addition  of  lime,  the  number  of 
bacteria  will  increase.  In  an  acid  soil,  the  addition  of 


Relation  of  Bacteria  to  Fertility.  177 

4000  pounds  of  limestone  per  acre  increased  the  number 
of  bacteria  from  440,000  per  gram  to  6,600,000  in  a 
period  of  seven  weeks. 

It  will  be  seen  that  whatever  makes  the  soil  a  better 
home  for  our  cultivated  plants,  increases  the  number  of 
bacteria  in  it.  The  question  at  once  comes  to  mind:  Is 
the  increased  fertility  as  shown  by  the  larger  crop,  the 
cause  of  the  growth  of  the  microscopic  plants,  or  is. the 
rapid  growth  of  the  bacteria  the  cause  of  greater  fertility, 
and  hence  the  larger  crop  of  corn  or  oats,  etc.  results  ?  As 
will  be  seen,  the  latter  is  the  true  statement.  Without 
great  bacterial  activity  in  the  soil,  large  crops  cannot  be 
grown. 

Higher  forms  of  life  in  the  soil.  Bacteria  are  not 
the  only  forms  of  life  that  live  in  the  soil  and  exert  an 
effect  on  its  properties.  In  acid  soils,  molds  may  grow 
luxuriantly.  The  soil  also  contains  various  kinds  of  tiny 
green  plants  found  so  abundantly  in  water,  the  green 
algae.  Still  larger  forms  of  life  are  of  great  importance, 
such  as  the  common  angle  worm,  that,  by  its  formation 
of  burrows,  brings  the  lower  layers  of  the  soil  to  the  sur- 
face, and  thus  in  the  course  of  a  few  years,  turns  the 
soil  over  as  completely  as  does  the  farmer's  plow.  The 
burrows  allow  the  air  to  penetrate  into  the  soil.  The 
land  under  permanent  grass  is  thus  aerated  and  culti- 
vated by  these  animal  forms.  These  and  all  other  low 
animal  forms  live  on  organic  matter ;  they  help  to  decom- 
pose it,  and  are  in  turn  decomposed  by  bacteria.  Sta- 
tistics that  have  been  collected  indicate  that  each  acre 
of  land  supports  as  much  life,  measured  in  pounds,  in  the 
shape  of  low  animal  forms,  as  the  farmer  keeps  in  the 
form  of  domestic  animals. 

The  soil  is.  thus,  not  a  dead  and  inert  mass,  but  some- 


178  Agricultural  Bacteriology. 

thing  teeming  with  forms  of  life  of  the  greatest  import- 
ance to  the  farmer.  It  is  a  manufacturing  establish- 
ment where  plant  food  is  made  from  raw  materials.  To 
furnish  the  workers  favorable  conditions  is  one  of  the 
problems  the  successful  tiller  of  the  soil  must  solve. 

Decomposition  of  organic  matter.  The  material  re- 
turned to  the  soil  under  natural  conditions  or  by  the 
farmer  in  the  form  of  stable  manure  or  the  crops  plowed 
under  (green  manuring)  is  organic  in  character,  i.  e., 
the  result  of  plant  and  animal  growth.  It  contains  the 
elements  that  are  necessary  for  succeeding  crops  of  vege- 
tation, but  in  such  a  form  that  they  cannot  be  used  until 
they  have  again  been  brought  to  the  same  condition  as 
when  they  were  first  taken  up  by  the  plant. 

The  organic  matter  added  to  the  soil  embraces  every 
conceivable  type  of  matter,  yet,  everything  serves  as  a 
food  for  some  form  of  life,  and  is  thus  decomposed  to 
some  extent.  Other  kinds  of  life  then  use  the  by-prod- 
ucts of  the  first  and  so  on  until  the  ultimate  stage  is 
reached  and  the  elements  can  be  again  made  use  of  by  a 
new  crop  of  wheat,  corn,  or  other  plant.  The  spoiling  of 
our  food  stuffs,  rotting  of  apples,  and  potatoes,  the  sour- 
ing of  milk,  the  putrefaction  of  meat,  and  the  rotting  of 
manure,  are  but  steps  in  this  great  series  of  decomposi- 
tion processes  carried  on  largely  by  bacteria. 

The  digestive  changes  occurring  in  all  kinds  of  ani- 
mals are  but  initial  steps  in  the  decomposition  of  organic 
matter,  since  the  material  given  off  from  their  bodies  is 
much  more  simple  than  the  food  absorbed  and  is  much 
more  easily  brought,  by  the  action  of  bacteria,  into  a 
form  that  can  be  used  by  the  green  plant. 

The  various  kinds  of  matter  added  to  the  soil  can  be 
divided  into  three  classes:  1st.  The  carbohydrates;  2nd. 


Relation  of  Bacteria  to  Fertility.  179 

the  protein  substances,  and  3rd.  the  fats.  The  first  are 
composed  of  carbon,  hydrogen,  and  oxygen  and  include 
such  substances  as  starch,  sugars,  cellulose,  and  woody 
fiber;  the  third  is  made  up  of  the  same  elements,  and  is 
represented  by  the  animal  and  vegetable  fats  and  oils. 
When  these  substances  are  completely  decomposed,  the 
elements  appear  as  water,  and  carbon  dioxid  (C02),  both 
of  which  can  be  used  by  the  plant. 

Protein  material  contains  in  addition  to  the  above  ele- 
ments nitrogen,  sulphur,  and  phosphorus.  The  end 
products  of  their  decomposition  are  carbon  dioxid,  water, 
ammonia,  free  nitrogen,  hydrogen  sulfide,  and  some  com- 
pound of  phosphorous.  The  ammonia,  hydrogen  sul- 
fide, and  phosphorous  compounds  must  be  further 
changed  by  certain  kinds  of  bacteria  before  the  green 
plant  can  use  the  nitrogen,  the  sulphur  or  the  phos- 
phorus. 

The  simple  end  products,  carbon  dioxid  and  water,  of 
the  bacterial  decomposition  of  organic  matter  do  not  in- 
terest us  further.  The  compounds  that  are  formed  dur- 
ing the  stages  of  decomposition  are  of  more  importance 
because  of  their  influence  on  the  soil. 

The  decomposition  is  carried  on  by  both  aerobic  and 
anaerobic  forms  of  bacteria.  The  great  distinction  be- 
tween their  work  is  that  the  work  of  the  first  is  complete ; 
the  most  simple  products  resulting,  such  as  carbon  dioxid, 
water,  and  ammonia.  The  material  acted  upon  dis- 
appears as  completely  as  though  it  had  been  burned. 
With  the  anaerobic  bacteria  the  work  is  not  wholly  fin- 
ished, but  a  part  of  the  material  remains  in  the  soil,  and 
forms  what  is  known  as  humus. 

Because  of  the  fact  that  in  cultivated  soil,  conditions 
are  favorable  for  the  aerobic  bacteria,  humus  does  not 


180  Agricultural  Bacteriology. 

accumulate.  On  the  other  hand  in  land  under  grass,  in 
woodland  and  in  wet  lands  the  anaerobic  bacteria  grow 
best.  Here  the  decomposition  of  the  vegetable  residue 
is  not  complete  and  the  humus  accumulates  in  the  soil. 
When  the  lowland  is  drained,  or  the  prairie  broken,  the 
aerobic  bacteria  begin  to  act  on  the  humus,  and  grad- 
ually destroy  it.  The  land  now  produces  more  than  in 
its  wild  state,  but  unless  organic  matter  is  returned  to  it 
as  manure,  etc.,  it  gradually  diminishes  in  fertility,  as 
has  been  so  well  shown  in  the  eastern  part  of  the  United 
States.  The  burning  of  the  straw  on  the  prairies  of  Miij- 
nesota  and  Dakota  is  one  way  in  which  the  fertility  of 
the  land  is  destroyed.  The  straw,  if  it  had  been  plowed 
under,  would  have  helped  to  keep  up  the  humus  content 
of  the  soil.  It  would  have  furnished  the  bacteria  food, 
and  the  result  would  have  been  a  much  less  rapid  de- 
crease in  fertility  in  those  fields,  the  soil  of  which  the 
settlers  thought  could  never  be  exhausted. 

In  a  sandy  soil,  the  aerobic  bacteria  grow  rapidly  and 
any  organic  matter  added  is  soon  completely  destroyed; 
while  in  a  close  soil  like  a  clay,  the  decomposition  pro- 
cesses go  on  much  more  slowly.  The  effect  of  a  heavy 
coating  of  manure  is  .often  to  be  noted  only  during  the 
season  in  which  it  is  applied  to  a  sandy  soil,  while  on  a 
clay  soil  it  may  manifest  its  effect  in  the  second  and 
even  in  the  third  year. 

In  some  kinds  of  farming,  the  farmer  cares  little  for 
the  fertility  of  the  soil,  but  wishes  one  that  will  allow 
the  rapid  growth  of  bacteria  which  are  to  decompose  the 
manure  that  is  added.  The  market  gardener,  with  an 
abundant  supply  of  manure  from  the  city,  wishes  such 
a  soil,  simply  a  place  for  the  bacteria  to  work  on  the  raw 
material  he  adds  to  the  soil. 


Relation  of  Bacteria  to  Fertility.  181 

The  green -plant  gets  its  supply  of  carbon  from  the 
carbon  dioxide  of  the  air.  Only  a  small  amount  is  pres- 
ent in  the  air  at  any  one  time,  so  little  in  fact  that  if  the 
supply  were  not  renewed  it  would  soon  be  exhausted. 
This  renewal  comes  from  the  decomposition  of  Organic 
matter  by  bacteria.  The  respiration  of  plants  and  ani- 
mals also  produces  carbon  dioxide.  The  burning  of  fuel 
also  frees  the  carbon  as  carbon  dioxide.  There  is  thus 
a  constant  passing  of  the  carbon  from  the  air  to  the  plant 
and  back  again  to  the  air  through  the  action  of  plants, 
animals  and  especially  the  bacteria  of  soil. 


CHAPTER  XX. 

EFFECT  OF  BACTERIA  ON  MINERALS  OF   THE 

SOIL. 

The  water  that  falls  on  the  soil  in  the  form  of  rain 
contains  no  mineral  matter  in  solution.  If  the  water 
from  a  well  or  that  which  runs  from  a  drain  is  exam- 
ined, it  will  be  found  to  contain  a  varying  amount  of  ma- 
terial that  has  been  dissolved  from  the  soil  through 
which  the  water  has  passed.  Most  of  the  mass  of  the 
soil  is  insoluble  in  pure  water,  hence  there  should  be 
found  but  a  very  small  amount  of  mineral  matter  in  the 
drainage  water  unless  there  are  factors  at  work  in  the 
soil,  changing  the  insoluble  minerals  into  soluble  com- 
pounds. It  has  been  seen  that  the  bacteria  render  the 
various  kinds  of  organic  matter  soluble,  and  that  the  prod- 
ucts formed  by.  their  action  are  water,  ammonia,  and  car- 
bon dioxide  together  with  some  less  important  products. 
Many  intermediate  pro<ducts  are  formed  in  the  decomposi- 
tion of  organic  matter  that  have  a  great  effect  on  the 
mineral  part  of  the  soil. 

In  the  decomposition  of  such  organic  substances  as 
sugars,  starches,  and  related  compounds,  acids  are 
formed,  as  lactic,  acetic,  and  butyric.  Carbon  dioxide 
when  dissolved  in  water  acts  as  a  weak  acid.  All  of 
these  acids  have  a  solvent  effect  on  the  different  minerals 
of  the  soil.  In  the  process  of  nitrification  a  strong  acid 
is  formed,  nitric  acid,  which  also  has  an  effect  on  the  soil 
particles. 


Effect  of  Bacteria  on  Minerals  of  the  Soil.     183 

Calcium.  This  important  element  is  present  in  the 
soil  in  the  form  of  calcium  carbonate  or  lime  stone,  which 
is  insoluble  in  pure  water,  but  owing  to  the  presence  of 
carbon  dioxide  and  organic  acids  in  the  soil,  the  water 
percolating  through  the  soil  carries  with  it  more  or  less 
calcium  carbonate.  The  water  which  comes  in  contact 
with  beds  of  lime  stone  is  called  "hard'7  water  because 
it  carries  in  solution  such  large  quantities  of  calcium  car- 
bonate. The  greater  the  amount  of  organic  matter 
added  to  the  soil,  the  greater  will  be  the  quantity  of  cais 
bon  dioxide  and  organic  acids  formed  by  bacterial  action 
and  the  more  rapidly  will  the  lime  be  removed  from  the 
soil. 

On  account  of  this  constant  solution  of  lime,  the  soil 
tends  to  become  acid,  which  condition  becomes  unfavor- 
able for  bacterial  action  and  the  soil  is  no  longer  fertile. 
The  farmer  finds  it  necessary  to  correct  this  acid  condi- 
tion by  adding  lime  to  the  soil  in  the  form  of  crushed 
lime  stone. 

The  dissolved  lime  passes  off  in  the  drainage  water  to 
the  sea,  where  it  is  used  by  marine  animals  in  forming 
their  shells.  As  these  organisms  die  they  gradually  sink 
to  the  bottom  of  the  sea,  forming  beds  of  lime  stone.  In 
some  great  movement  of  the  crust  of  the  earth  these  are 
raised  above  the  surface,  and  are  subjected  to  the  action 
of  weathering  and  influence  of  biological  changes.  Thus 
the  movement  of  lime  from  land  to  sea  and  sea  to  land 
goes  on. 

Phosphorus.  The  phosphorus  of  the  soil  is  largely 
in  the  form  of  calcium  phosphate,  which,  like  calcium 
carbonate,  is  insoluble  in  pure  water  but  which  is  easily 
dissolved  in  water  which  is  acid  in  reaction.  Even  car- 
bonic acid  will  change  it  to  a  soluble  form  in  the  same  way 


184  Agricultural  Bacteriology. 

that  lime  stone  is  made  soluble.  Phosphorus  is  thus  con- 
stantly lost  from  the  soil. 

The  fertility  of  soil  may  be  limited  through  the  fact 
that  the  soil  does  not  contain  phosphorus  in  any  form,  or 
because  the  phosphorus  it  does  contain  is  not  rendered 
available  by  solution.  Phosphorus  may  be  added  to  the 
scil  in  the  form  of  bone-meal,  phosphate  rock  (floats,  or 
calcium  phosphate),  superphosphate  (acid  phosphate). 
Of  these  only  the  last  is  immediately  available  to  the 
plant,  as  the  other  compounds  are  the  same  as  the  phos- 
phorus already  present  in  the  soil.  Their  addition  alone 
to  a  soil  that  is  lacking  in  available  phosphorus  has  no 
effect  whatever.  If  added  in  connection  with  a  large 
amount  of  organic  matter,  as  barn  yard  manure,  or  a 
crop  that  is  plowed  under,  the  insoluble  phosphates  are 
made  available  because  the  organic  material  furnishes 
food  for  the  bacteria,  which  as  a  result  of  their  growth 
form  acids  that  render  soluble  the  calcium  phosphate. 
The  addition  of  rock  phosphate  to  sandy  land  or  to  land 
low  in  humus  is  of  little  use.  Sprinkling  "floats"  on 
the  manure  as  it  is  made  is  an  excellent  way  of  adding 
the  phosphate  to  the  soil.  The  insoluble  phosphate  is 
thus  brought  in  intimate  contact  with  decomposing  or- 
ganic matter  and  is  gradually  rendered  soluble. 

There  is  need  of  an  abundant  supply  of  available  phos- 
phorus in  the  soil  not  only  for  the  green  plant  but  for 
some  forms  of  bacteria  that  are  very  beneficial  to  the 
farmer.  The  different  kinds  of  nitrogen-fixing  bacteria, 
both  those  that  grow  in  the  nodules  of  the  leguminous 
plants  and  those  in  the  soil  itself,  develop  most  luxuri- 
antly only  when  phosphorus  is  available. 

The  fertility  of  a  soil  may  be  low  because  the  phos- 
phorus it  contains  is  not  being  rendered  available.  Un- 


Effect  of  Bacteria  on  Minerals  of  the  Soil.        185 

<ier  such  conditions,  the  question  of  fertility  may  not  be 
affected  so  much  by  the  addition  of  more  phosphate  as  by 
the  incorporation  of  organic  matter  that  will  render 
available  the  phosphorus  which  is  already  present  in  the 
soil. 

Potassium.  The  content  of  soils  in  this  important 
element  is  usually  very  high.  A  soil  may  contain  many 
thousand  pounds  of  potassium  per  acre  and  yet  so  little 
of  it  be  made  available  to  the  plant  that  the  soil  will  re- 
spond to  the  addition  of  a  potash  fertilizer.  Potassium 
is  rendered  soluble  by  bacterial  action  in  the  same  man- 
ner as  are  calcium  and  phosphorus.  The  growth  of  the 
nitrogen-fixing  bacteria  is  possible  only  when  potassium 
is  available.  «, 

Sulphur.  The  sulphur  that  is  taken  from  the  soil  by 
the  green  plant  in  the  form  of  calcium,  potassium  or  so- 
dium sulphate  is  rendered  available  to  the  plant  once 
more  through  the  action  of  bacteria.  When  organic 
matter,  either  of  plant  or  animal  origin,  undergoes  de- 
composition, the  sulphur  is  changed  into  hydrogen  sul- 
phide, a  gas  that  is  one  of  the  causes  of  the  offensive 
odors  coming  from  putrefying  materials.  This  gas  is 
poisonous  to  the  green  plant.  It  is,  however,  utilized  by 
the  sulphur  bacteria  which  are  found  most  abundantly 
in  sulphur  springs.  They  also  occur  in  the  soil  where 
they  use  the  hydrogen  sulphide  formed  from  decompos- 
ing matter,  changing  it  to  sulphates,  the  form  in  which 
it  can  be  again  used  by  the  plant. 

The  characteristic  odor  of  the  soil  has  been  shown  to 
"be  due  to  a  compound  formed  by  the  growth  of  a  certain 
<jlass  of  bacteria  in  the  soil. 


CHAPTER  XXI. 

AMMONIFICATION,  NITRIFICATION  AND  DENIT- 
RIFICATION. 

The  green  plant  takes  the  carbon  that  it  needs  for  its 
growth  from  the  air  in  the  form  of  carbon  dioxide. 
During  each  growing  period  there  is  an  immense  amount 
of  this  compound  removed  from  the  air,  but  which  how- 
ever is  constantly  replenished  by  various  factors  among 
which  the  bacteria  are  very  important.  Through  the 
work  of  micro-organisms  and  the  respiration  of  plants 
and  animals  the  carbon  bound  up  in  the  organic  matter 
is  again  made  ready  for  the  use  of  the  plant. 

The  nitrogen  that  the  plant  demands  for  its  growth 
is  taken  from  the  soil  in  the  form  of  nitrates.  The 
amount  of  combined  nitrogen  in  the  soil  is  small,  and 
unless  there  are  factors  at  work  that  shall  restore  the 
nitrogen  found  in  the  bodies  of  plants  and  animals  to  a 
form  in  which  it  can  again  be  used  by  the  plant,  the  soil 
would  soon  be  depleted  of  this  element.  The  immense 
vamount  of  free  nitrogen  in  the  air,  amounting  to  at  least 
35,000  tons  over  each  acre,  is  not  available  for  the  green 
plant,  except  under  special  conditions  that  will  be  dis- 
cussed in  a  subsequent  chapter. 

The  nitrogen  of  the  soil  is  in  the  humus  and  is  not 
available  to  the  plant  but  must  be  worked  over  and 
changed  to  a  form  in  which  the  green  plant  can  use  it, 
just  as  the  nitrogen  added  to  the  soil  in  the  green  crop 
or  in  manure  must  pass  through  a  complex  series  of 
changes  to  be  of  use  to  the  plant  again. 


Ammonification.  187 

Ammonification.  When  organic  matter  containing 
nitrogen  is  decomposed  by  bacterial  action,  a  part  of  the 
nitrogen  is  returned  to  the  air  as  free  nitrogen.  This  is- 
of  course  lost  so  far  as  the  soil  is  concerned.  The  larger 
part  of  the  nitrogen  is  changed  to  ammonia  after  pass- 
ing through  a  complex  series  of  changes.  The  presence 
of  ammonia  can  often  be  noted  about  heaps  of  decompos- 
ing matter,  especially  piles  of  horse  manure.  The  pro- 
duction of  ammonia  from  organic  matter  is  due  to  the 
work  of  many  classes  of  bacteria  widely  distributed  in 
the  soil.  These  bacteria  belong  to  both  the  aerobic  and 
anaerobic  classes,  thus  making  possible  the  process  of  am- 
monification  under  widely  diverse  conditions  as  to  pres- 
ence or  absence  of  oxygen.  There  is  usually  no  lack  of 
some  of  the  various  kinds  of  ammonifying  bacteria  in  the 
soil,  and  the  conditions  under  which  they  work  are  so 
varied  that  the  farmer  does  not  have  to  consider  means 
of  favoring  their  action.  The  work  which  they  do  is  ab- 
solutely essential  to  the  fertility  of  the  soil,  since  it  is 
one  of  the  steps  in  the  transformation  of  the  nitrogen  to 
an  available  form  for  the  plant.  Soils  have  been  studied 
in  which  it  was  thought  that  the  cause  of  the  low  fer- 
tility was  the  lack  of  ammonifying  bacteria. 

Nitrification.  Under  the  action  of  these  bacteria  the 
nitrogen  of  decomposing  matter  is  rapidly  changed  to 
ammonia.  Plants  can  not  use  nitrogen  in  this  form  to 
advantage.  Some  kinds  of  plants  can  cover  part  of  their 
need  for  nitrogen  from  this  source,  others  can  not  use 
ammonia  at  all.  It  is  therefore  necessary  for  the  nitro- 
gen to  be  still  farther  changed  by  the  action  of  specific 
organisms,  the  nitrifying  bacteria.  There  are  to  be  found 
in  nearly  every  soil  two  classes  of  the  nitrifying  organ- 
isms, one  which  changes  the  nitrogen  of  ammonia  to  ni- 


188  Agricultural  Bacteriology. 

trous  acid,  the  other  the  nitrous  acid  to  nitric  acid  which 
when  combined  with  lime  forms  calcium  nitrate.  If  the 
second  class  of  bacteria  is  not  present  in  the  soil,  it  can 
not  be  fertile,  since  plants  can  not  make  use  of  nitrogen 
in  the  form  of  nitrites. 

The  absence  or  limited  amount  in  the  soil  of  any  of  the 
elements  necessary  for  plant  growth  may  be  the  cause 
of  the  low  fertility  of  a  soil.  The  condition  most  likely 
to  be  associated  with  a  reduced  yield  is  lack  of  nitrogen. 
The  nitrates  are  very  soluble  in  water  and  are  easily 
leached  from  the  soil.  Those  formed  during  one  season 
are  removed  during  the  winter  and  spring,  and  as  there 
is  no  accumulation  of  available  nitrogen  in  the  soil  the 
supply  is  rarely  much  in  excess  of  the  needs  of  the 
plant.  It  is  thus  necessary  that  enough  nitrogen  be  ren- 
dered available  during  the  growing  season  to  supply  the 
needs  of  a  luxuriant  crop.  If  the  process  of  nitrification 
is  retarded,  the  crop  will  be  a  meager  one.  It  is  of  the 
greatest  importance  that  the  farmer  be  acquainted  with 
the  conditions  that  favor  the  process  of  nitrification  in  the 
soil,  for  unless  the  crop  of  nitrifying  bacteria  in  his  soil 
is  large,  the  yield  of  corn,  oats,  etc.,  can  not  be  a  profit- 
able one. 

Conditions  for  nitrification.  The  nitrifying  bacteria 
are  aerobic.  They  grow  best  in  an  open  textured  and 
well  aerated  soil.  In  one  that  is  close  and  dense,  the 
process  of  nitrification  is  retarded;  in  a  water  logged  soil 
it  does  not  go  at  all.  By  draining  a  field  the  water  is 
removed,  air  is  drawn  into  the  soil  and  nitrification  goes 
on  rapidly.  Cultivation  also  allows  the  air  to  penetrate 
the  soil  more  thoroughly  and  favors  nitrification.  It  will 
be  noted  that  the  largest  yields  are  in  the  case  of  the  so- 
called  cultivated  crops  rather  than  with  the  grasses  and 


Xitrification.  189 

grains.  This  is  due  in  no  small  measure  to  the  larger 
amount  of  nitrogen  rendered  available  because  of  the 
favorable  conditions  for  the  nitrate-forming  bacteria  in 
scil  which  is  frequently  stirred. 

It  is  essential  that  the  soil  shall  contain  some  sub- 
stance, as  lime,  to  combine  with  the  nitric  acid  formed, 
otherwise  the  soil  soon  becomes  acid  and  nitrification  is 
no  longer  possible.  In  a  marshy  soil  the  process  may  go 
on  slowly  or  not  at  all.  If  an  application  of  lime  is  made 
and  the  acidity  neutralized,  nitrification  begins.  In 
such  a  soil  the  process  is  also  favored  by  drainage  and 
cultivation  since  the  aerobic  forms  of  life  gradually  de- 
stroy the  acid  products  that  have  been  formed  by  the  an- 
aerobic bacteria. 

The  change  of  ammonia  to  nitrates  can  not  go  on  in 
the  presence  of  large  amounts  of  organic  matter,  as  for 
example  in  a  manure  heap.  The  nitrifying  bacteria  are 
unable  to  grow  in  a  very  dry  soil.  The  process  of  nitri- 
fication reaches  its  maxium  in  the  soil  during  the  sum- 
mer, especially  during  June  and  July,  when  the  need  of 
the  growing  crop  for  nitrates  is  greatest.  It  goes  on, 
however,  during  the  fall  and  to  some  extent  as  long  as 
the  ground  is  not  frozen.  The  reason  for  the  greater 
rapidity  of  the  formation  of  nitrates  during  the  early 
summer  is  found  in  the  favorable  temperature  condi- 
tions, together  with  the  large  amount  of  ammonia  that 
is  formed  from  the  decomposition  of  the  previous  year's 
crop. 

The  sodium  nitrate  that  is  used  for  fertilizer  and  in  the 
chemical  industries  is  obtained  in  Chile  where  there  are 
large  deposits.  These  are  supposed  to  have  been  formed 
by  the  decomposition  of  sea  weed  under  such  conditions 
that  the  resulting  nitrate  was  not  leached  away.  Im- 


190  Agricultural  Bacteriology. 

mense  amounts  of  nitrates  are  used  in  the  manufacture 
of  explosives  as  gun  powder,  nitroglycerine,  etc.  Be- 
fore the  discovery  of  the  Chilean  deposits,  the. nitrate 
needed  for  such  purposes  was  largely  made  on  the  salt- 
peter plantations.  A  mixture  of  earth  and  organic  mat- 
ter of  any  kind  was  made  and  placed  in  a  pile  which  was 
protected  from  leaching.  The  air  was  allowed  access  to 
the  inside  of  the  pile  by  placing  brush  wood  in  it.  The 
-nitric  acid  formed  was  neutralized  by  mixing  lime  stone 
with  the  soil  or  by  the  addition  of  soapy  water.  When 
the  process  was  completed,  the  entire  pile  was  leached 
and  the  nitrate  obtained  by  evaporating  the  water.  The 
deposits  in  Chile  will  soon  be  exhausted,  but  it  is  certain 
that  methods  will  be  found  by  which  the  nitrogen  of  the 
.air  can  be  brought  into  combination  as  nitrates,  and  it 
will  not  be  necessary  to  rely  on  the  action  of  bacteria  for 
the  nitric  acid  needed  in  the  industries,  and  as  fertilizers. 
The  farmer  must  always  depend  upon  the  action  of  this 
class  of  bacteria  in  order  to  obtain  the  nitrates  needed  by 
the  various  crops  grown  by  him. 

Denitrification.  In  the  broadest  sense  denitrification 
may  include  any  process  due  to  micro-organisms  by 
which  the  nitrogen  available  to  the  plant,  i.  e.,  that  con- 
tained in  nitrates,  is  changed  so  that  it  is  less  available  or 
rendered  unavailable.  There  are  a  number  of  processes 
by  which  this  is  accomplished.  The  process  may  be  the 
reverse  of  nitrification,  the  nitrates  being  reduced  to  ni- 
trites and  to  ammonia.  The  bacteria  responsible  for  this 
-action  can  act  only  in  the  absence  of  air  and,  while  they 
are  always  present  in  the  soil,  they  do  not  usually  mani- 
fest themselves.  During  a  wet  spell  in  the  summer,  the 
•soil  may  be  so  saturated  with  water  and  hence  contain  so 
little  air  that  these  bacteria  can  destroy  the  nitrates  pres- 


Denitrification.  191 

«nt.  If  the  wet  weather  continues  for  any  length  of  time, 
the  crops,  especially  those  that  need  large  amounts  of  ni- 
trates and  can  not  use  nitrogen  in  the  form  of  ammonia  at 
all,  begin  to  suffer  from  nitrogen  hunger  which  is  shown 
by  the  yellow  color  of  the  leaves  in  place  of  the  dark  green 
of  the  well  nourished  plant.  As  soon  as  the  water  leaches 
from  the  soil  and  air  is  drawn  into  the  same,  the  nitrify- 
ing bacteria  change  the  nitrites  and  ammonia  back  to 
nitrates.  In  the  lower  parts  of  a  field  the  conditions 
favorable  for  denitrification  may  continue  so  long  that 
the  crop  is  permanently  injured.  This  property  of  re- 
ducing nitrates  is  a  very  common  one  among  the  soil  bac- 
teria. 

In  the  process  just  described  the  nitrogen  is  not  per- 
manently lost.  A  more  important  process  is  one  in 
which,  by  the  action  of  bacteria,  the  nitrogen  of  nitrates 
is  set  free  and  passes  into  the  air.  The  bacteria  able  to 
do  this  are  always  present  in  the  soil.  They  demand  for 
their  action  the  absence  of  oxygen,  and  an  abundance  of 
organic  matter,  as  well  as  the  presence  of  nitrates.  They 
are  of  small  significance  in  the  soil  for  the  conditions 
necessary  for  their  action  are  not  likely  to  obtain,  /^They 
are  especially  abundant  in  fresh  manure,  but  much  less 
so  in  rotted  manure.  If  a  large  amount  of  msanure  is 
added  to  the  soil  together  with  sodium  nitrate,  as  may  be 
done  in  gardening  or  in  green  house  work,  the  nitrate 
may  be  destroyed  by  the  action  of  this  class  of  bacteria. 

It  will  be  seen  that  the  conditions  favoring  dentrifica- 
tion  are  the  opposite  of  those  favorable  to  nitrification. 
The  farmer  by  frequent  cultivation,  by  drainage,  and  by 
maintaining  the  soil  in  good  tilth,  favors  the  beneficial 
process  and  retards  the  harmful  one.  It  is  fortunate 
that  those  conditions  that  are  most  favorable  for  the  for- 


392  Agricultural  Bacteriology. 

mation  of  nitrates  are  the  ones  that  are  naturally  de- 
manded by  the  green  plant  in  normal  growth. 

Some  of  the  soil  bacteria  derive  their  supply  of  nitro- 
gen from,  the  same  source  as  do  the  green  plants,  i.  e., 
the  nitrates.  If  these  forms  are  abundant  in  the  soil, 
they  will  compete  with  the  plants  for  the  nitrate  present. 
Since,  as  has  been  indicated,  the  nitrogen  is  most  often 
the  limiting  factor  in  plant  growth,  it  is  important  that 
as  much  of  it  be  reserved  for  the  crop  as  possible.  The 
presence  of  weeds  in  the  field  may  limit  the  crop  because 
they  use  a  portion  of  the  nitrogen  that  would  otherwise 
be  available  for  the  crop.  The  bacteria  that  use  the  ni- 
trogen of  nitrates  may  limit  the  crop  in  the  same  manner. 
The  conditions  that  favor  their  action  and  their  import- 
ance in  the  soil  are  problems  yet  unsolved. 

During  the  decomposition  of  organic  matter  of  all 
kinds  some  of  the  nitrogen  is  set  free.  It  is  not  known 
that  the  farmer  can  prevent  this  in  the  soil,  but  in  the 
handling  of  the  most  important  by-product  of  the  farm, 
the  manure,  much  can  be  done  to  avoid  this  loss. 

Conservation  of  nitrogen.  It  is  desirable  to  conserve 
the  supply  of  nitrogen  in  the  soil  as  much  as  possible 
since  to  restore  the  nitrogen  supply  is  a  slow  process 
when  the  natural  factors  are  relied  on,  while  to  furnish 
the  amounl  needed  by  a  crop  in  the  form  of  commercial 
fertilizers  would  be  too  expensive. 

During  the  growing  season  nitrates  are  being  con- 
stantly formed  and  are  as  rapidly  used  by  the  crop.  In 
the  more  fertile  soils  a  greater  amount  of  nitrate  may  be 
formed  than  is  needed  by  the  plant.  Some  of  this  is 
taken  up  by  the  plant  but  it  not  used.  It  accumulates 
in  the  tissues  as  potassium  nitrate.  It  has  been  thought 
by  some  that  the  corn  stalk  disease  previously  described 


Conservation  of  Nitrogen.  193 

was  due  to  poisoning  by  the  large  amounts  of  this  com- 
pound in  the  corn.  While  this  is  probably  not  true,  the 
excess  of  nitrate  taken  up  by  the  plant  not  only  makes 
the  corn  fodder  less  valuable  but  depletes  the  soil  of  ni- 
trogen. The  nitrate  not  taken  up  by  the  plant  is  leached 
from  the  soil  during  the  winter  and  spring  and  is  lost. 

The  ideal  condition  would  be  to  have  the  nitrates 
formed  at  the  time  they  are  needed  by  the  plant  and  to 
have  no  excess.  But  this  is  not  possible,  an  excess  must 
be  formed  in  order  to  obtain  a  maximum  crop  since  the 
roots  of  the  plants  do  not  reach  each  soil  particle.  It  is 
estimated  that  for  each  pound  of  nitrogen  removed  from 
the  soil  in  the  crop,  four  pounds  are  lost  in  drainage 
water.  The  farmer  can  do  something  to  conserve  the 
nitrogen  of  his  soil.  If  a  crop  has  been  removed  in  late 
summer  or  early  fall,  there  will  be  nothing  to  use  the 
nitrate  that  will  be  formed,  hence  it  will  be  lost  during 
the  winter.  If  a  cover  crop  had  been  planted  it  would 
have  absorbed  the  nitrate,  building  the  nitrogen  up  into 
its  tissue  and  preventing  its  loss  from  the  soil.  If  the 
cover  crop  is  plowed  under  in  the  spring,  it  will  be  de- 
composed, and  not  only  the  nitrogen  it  contains,  but  the 
phosphorus  and  potash  as  well,  rendered  available  for 
the  next  crop.  In  orchards  not  under  sod  the  cover  crop 
is  especially  beneficial.  If  the  cover  crop  is  one  of  the 
leguminous  plants,  the  soil  may  even  be  enriched  in  ni- 
trogen as  will  be  seen  later. 

It  is  now  recognized  that  the  process  of  fallowing  the 
land  is  an  excellent  means  of  robbing  the  soil  of  its  nitro- 
gen because,  while  the  soil  is  bare,  the  frequent  stirring 
establishes  favorable  conditions  for  nitrification,  but  as 
there  is  no  crop  present  to  use  the  nitrates  which  are 
formed  they  are  lost  in  the  drainage  water. 


194  Agricultural  Bacteriology. 

The  material  that  is  turned  under  in  the  cover  crop 
furnishes  food  for  innumerable  bacteria,  and  by-prod- 
ucts of  their  growth  act  on  the  mineral  part  of  the  soil, 
rendering  the  lime,  potassium,  and  phosphorus  available 
to  the  green  plant.  It  also  furnishes  food  for  a  class  of 
bacteria  to  be  described  in  a  subsequent  chapter  that  aid 
in  maintaining  the  nitrogen  content  of  the  soil.  A  part 
of  the  organic  matter  of  the  crop  plowed  under  accumu- 
lates in  the  soil  as-  humus  which  has  a  most  favorable 
effect  on  the  physical  condition  of  the  soil.  In  the  con- 
servation of  the  nitrogen  of  the  soil  it  is  apparent  that 
the  best  practice  is  not  to  allow  the  land  to  lie  idle,  but 
to  keep  it  covered  with  a  crop. 


CHAPTER  XXII. 
FIXATION  OF  NITROGEN. 

At  the  time  when  life  first  appeared  on  the  earth  the 
soil,  of  course,  contained  no  organic  matter  for  such  ma- 
terial is  the  product  of  living  things,  plants  and  animals. 
The  soil  was  presumably  composed  of  clay,  sand,  and 
gravel,  the  result  of  the  processes  of  disintegration  of 
the  original  rocks  of  which  the  earth  was  composed. 
During  the  thousands  and  thousands  of  years  that  have 
passed,  organic  matter  has  been  accumulating  in  the  soil 
because  all  of  the  material  that  the  soil  produced,  vege- 
table or  animal,  was  returned  to  it.  This  material  has 
been  decomposed  by  the  bacteria  and  other  forms  of  life 
with  the  production  of  the  various  substances  that  have 
been  previously  mentioned.  A  part  of  the  organic  mat- 
ter has  not  been  completely  decomposed,  but  remains  in 
the  soil  in  the  material  called  humus.  On  account  of  its 
effect  on  the  physical  properties  of  the  soil,  and  because 
it  is  a  source  of  nitrogen,  humus  is  one  of  the  most  im- 
portant constituents  of  the  soil.  It  is  not  certain  that 
the  soil  at  the  time  life  began  to  exist  on  the  earth  con- 
tained any  nitrogen.  The  question  at  once  arises  as  to 
how  the  present  store  of  nitrogen  found  in  the  soil  has 
been  gathered  from  the  air. 

It  is  evident  that  soils  under  natural  conditions  tend 
to  accumulate  nitrogen  until  some  of  them  contain  such 
large  amounts  as  are  found  in  the  soils  of  our  western 
prairies.  Under  artificial  conditions,  as  under  cultiva- 


196  Agricultural  Bacteriology. 

tion,  the  soil  tends  to  become  poorer  and  poorer  in  nitro- 
gen, because  the  supply  of  this  element  is  being  used  by 
succeeding  crops  of  plant  life,  and  unless  some  means 
are  taken  to  restore  the  supply,  the  soil  soon  becomes  a 
barren  one.  If  every  thing  that  the  soil  produced  was 
returned  to  it,  its  fertility  could  be  maintained  indefi- 
nitely. The  soil  in  certain  parts  of  Japan  and  China  has 
been  cultivated  for  thousands  of  years  and  is  today  as 
fertile  as  ever  because  every  bit  of  the  waste  matter  of 
human  and  animal  life  has  been  returned  to  it,  and  has 
not  been  sent  down  to  the  sea  in  the  form  of  sewage  or 
exported  to  other  lands  in  the  form  of  raw  and  manufac- 
tured products,  as  is  being  done  in  our  own  country.  It 
seems  impractical  for  us  to  be  as  careful  as  are  the  peo- 
ples mentioned  in  returning  to  the  soil  all  waste  matter. 
Yet  it  is  absolutely  necessary  for  us  to  maintain  the  ni- 
trogen supply  of  the  soil  in  every  possible  way,  for  this 
is  the  element  that  is  most  likely  to  be  lost,  and  the  one 
which  is  the  most  costly  to  replace  in  the  form  of  com- 
mercial fertilizers. 

The  air,  composed  as  it  is  of  four-fifths  of  nitrogen  and 
one  fifth  of  oxygen,  furnishes  the  source  from  which  it 
becomes  possible  to  draw  unlimited  supplies  of  nitrogen. 
The  nitrogen  of  the  air  is  not  directly  available  for  most 
green  plants.  It  is,  however,  much  more  economical  for 
the  farmer  to  learn  how  to  utilize  this  supply  than  to 
rely  for  his  store  of  nitrogen  on  the  commercial  ferti- 
lizers that  may  be  purchased. 

Fixation  of  nitrogen.  Within  the  last  few  years 
methods  for  the  fixation  of  the  nitrogen  of  the  air  by 
electrical  means  have  been  perfected.  "Where  cheap 
power  can  be  procured,  as  near  water-falls,  nitrogenous 
fertilizers  can  be  made  cheap  enough  to  compete  with  the 


Fixation  of  Nitrogen.  197 

natural  product  from  Chile.  It  is  thus  certain  that  life 
\vill  never  cease  to  exist  on  the  earth  because  the  supply 
of  combined  nitrogen  has  been  used  up  for  the  illimitable 
store  of  the  free  nitrogen  of  the  air  will  always  serve  as  a 
supply  in  the  future  as  it  has  in  the  past.  Present  farm 
practice,  however,  in  the  hands  of  many  is  blindly  rob- 
bing the  soil  of  these  accumulations  by  natural  agencies; 
in  other  words  we  are  living  on  the  capital , which  has 
been  stored  up.  When  so  handled,  it  is  only  a  question 
of  time  before  our  capital  will  be  exhausted,  and  then  re- 
liance must  be  placed  on  the  nitrogen  that  is  returned 
to  the  soil  in  the  form  of  manures  and  on  that  fixed  by 
natural  means,  in  order  to  furnish  the  necessary  amount 
for  the  crops. 

A  consideration  therefore  of  the  natural  agencies  that 
are  fixing  nitrogen  in  the  soil  and  elsewhere  is  important 
and  especially  those  that  are  susceptible  of  control  by 
man.  Every  flash  of  lightning  causes  some  of  the  nitro- 
gen of  the  air  to  combine  with  oxygen,  forming,  with  the 
water  in  the  air,  nitric  acid  which  is  brought  to  the  soil 
in  the  rain  water.  In  this  way  a  small  amount  of  nitro- 
gen is  added  to  every  acre  each  year  but  a  comparatively 
inappreciable  quantity  when  compared  with  the  needs  of 
the  crop. 

The  most  important  agencies,  however,  that  are  con- 
cerned in  the  fixation  of  nitrogen  of  the  air  are  the  bac- 
teria that  are  found  in  every  soil.  There  are  three  types 
known  at  the  present  time,  one  of  which  fixes  nitrogen  by 
the  help  of  a  certain  kind  of  green  plants,  the  legumes, 
the  remaining  kinds  being  able  to  do  so  independently. 
If  conditions  are  not  favorable  for  the  growth  of  these 
bacteria  in  the  soil  practically  no  increase  in  nitrogen 
Avill  occur.  It  is  thus  essential  to  learn  what  conditions 


198  Agricultural  Bacteriology. 

favor  their  growth  and  to  seek  to  establish  such  in  the 
soil. 

Leguminous  plants.  It  has  been  known  since  the 
days  of  the  early  Romans  that  leguminous  plants  had  a 
favorable  effect  on  the  soil  and  for  this  reason  they  were 
included  in  nearly  all  systems  of  crop  rotation.  This 
favorable  effect  of  the  legumes  was  explained  in  many 
ways.  Some  claimed  that  because  of  their  deep  roots, 
they  were  able  to  reach  plant  food  that  was  ordinarily 


FIG.  19.- — LEGUMINOUS  PLANTS. 

Clover  growing  in  soil  free  from  nitrogen.  In  jar  No.  6  the 
soil  is  also  free  from  the  nodule-forming  bacteria;  in  jar 
No.  5  the  soil  contains  an  abundance  of  them. 

inaccessible  or  because  of  their  abundant  supply  of  leaves, 
they  drew  more  food  from  the  air.  It  was  not  until  late 
in  the  last  century  that  the  real  reason  was  discovered. 

It  had  been  noted  that  many  of  the  leguminous  plants 
often  had  peculiar  nodules  or  swellings  on  their  roots 
which  were  regarded  as  harmful  to  the  plant,  also 'that 
leguminous  plants  would  grow  on  sandy  soils  that  were 
too  poor  to  produce  crops  of  ordinary  grains.  It  was 


Fixation  of  Nitrogen.  199 

at  last  discovered  that  the  ability  of  leguminous  plants 
to  grow  under  these  conditions  was  connected  with  the 
presence  of  nodules  on  their  roots  and  that  in  the  ab- 
sence of  such  structures,  the  legumes  required  as  fertile 
a  soil  in  order  to  produce  a  good  crop  as  did  any  other 
plant.  It  was  also  found  that  where  the  nodules  did  not 
develop  the  legume,  instead  of  having  a  beneficial  effect 
on  the  soil,  left  it  less  fertile,  the  same  as  any  other  plant. 
It  was  also  found  that  when  the  nodules  developed  on 
the  roots,  the  beneficial  effect  was  due  to  the  fact  that  the 
soil  contained  more  nitrogen  after  the  crop  had  been  re- 
moved than  before,  even  though  that  portion  of  the  crop 
which  was  removed  contained  a  considerable  amount  of 
nitrogen. 

Cause  of  the  nodules.  The  root  hairs  of  the  plant 
which  are  exceedingly  delicate  and  unprotected  by  any 
thick  membrane  become  infected  with  the  legume  bac- 
teria which  are  in  the  soil.  These  cause  an  increased  cell 
growth  at  the  point  of  entrance,  thus  forming  the  nodule 
or  tubercle  which  becomes  filled  with  bacterial  cells.  In 
some  way  not  well  understood,  these  organisms  are  able 
to  fix  the  nitrogen  of  the  soil  air  and  build  it  up  into  such 
a  form  that  the  green  plant  can  use  it. 

Through  these  discoveries  the  peculiar  effect  of  the 
leguminous  plants  on  the  fertility  of  the  soil  and  the 
ability  of  the  plant  to  grow  in  the  absence  of  combined 
nitrogen  was  explained.  It  is  evident  that  the  farmer 
should  be  certain  that  any  legume  he  grows  should  pos- 
sess an  abundance  of  nodules  on  the  roots  so  that  he  will 
receive  the  maximum  benefit  from  the  crop. 

Different  kinds  of  legumes  require  different  kinds  of 
bacteria,  as  for  instance  the  organisms  that  normally  in- 
fect clover  have  no  influence  on  alfalfa  or  vice  versa.. 


200  Agricultural  Bacteriology. 

In  some  cases  this  specific  character  does  not  obtain. 
For  example  the  organisms  inhabiting  the  ordinary 
sweet  clover  are  able  to  infect  alfalfa  but  not  the  com- 
mon red  or  white  clovers.  It  is  thus  necessary  to  see 
that  the  soil  contains  the  right  kind  of  bacteria,  and  if 
they  are  not  present  naturally  in  the  soil,  it  must  be  in- 
oculated with  them. 

Kinds  of  legumes.  There  are  many  thousands  of 
legumes  both  wild  and  cultivated,  varying  in  size  from 
tiny  plants  to  large  trees,  all  of  which  bear  nodules  on 
the  roots.  In  the  native  flora  of  every  type  of  soil  are 
to  be  found  representatives  of  this  group  of  plants.  The 
ordinary  beggar-weed,  the  sensitive  plant,  and  the  wild 
lupines  are  some  of  the  native  legumes.  All  of  the  clov- 
ers, red,  crimson,  and  white,  the  sweet  clovers,  both  white 
and  yellow,  alfalfa,  all  of  the  peas,  such  as  garden,  sweet, 
field,  and  cowpeas,  the  various  kinds  of  beans,  soy  beans, 
lupines,  vetches  and  serradella,  and  the  pea-nut  are 
among  the  most  important  of  the  cultivated  legumes. 

The  legumes  are  found  growing  on  all  types  of  soils, 
in  marshy  soils,  in  sand  and  clay,  in  those  that  contain 
much  lime  and  in  those  free  from  it.  All  types,  how- 
ever, bear  nodules,  so  the  bacteria  capable  of  developing 
under  these  conditions  are  wide  spread  and  abundant. 

Form  and  appearance  of  nodules.  The  nodules  vary 
in  size  and  appearance  depending  on  the  species  of  plant. 
Those  on  the  clovers  are  very  small,  about  the  size  of  a 
large  pin  head,  and  oval  in  form,  with  a  smooth  surface. 
The  alfalfa  nodules  are  much  like  those  of  clover  but 
have  a  tendency  to  grow  in  finger-like  clusters.  The 
nodules  of  beans  are  round,  rough  on  the  surface,  and 
much  larger  than  those  on  clovers,  some  times  reaching 
the  size  of  a  large  cherry.  The  nodules  on  peas  are  very 


Fixation  of  Nitrogen. 


201 


similar  in  appearance  and  size  to  those  found  on  beans. 
The  size  of  the  nodules  depends  on  the  number  on  the 
plant.  When  few,  the  nodules  are  likely  to  be  large,  when 
more  numerous  the  size  is  smaller.  The  total  mass  of 


FIG.  20. — TUBERCLES  ox  SOY  BEANS. 
B.   the   roots  are  free  from  tubercles;  C.  the  roots 
are  studded  with  large  tubercles.     Large  masses 
of  them  are  to  be  seen  on  the  main  root. 

the  nodules  may  make  up  one  fourth  of  the  weight  of  the 
root  system. 

On  cutting  the  nodules  open  it  will  be  found  that  the 
color  of  those  that  are  small  is  pale  red  or  pink,  unlike 
the  color  of  any  other  part  of  the  plant.  If  a  little  of 
the  content  of  the  nodule  is  examined  under  the  micro- 


202  Agricultural  Bacteriology. 

scope,  it  will  be  seen  to  be  filled  with  innumerable  bac- 
teria that  move  about  in  the  water  in  which  the  contents, 
of  the  nodule  has  been  placed.  The  nodules  are  usually 
found  near  the  top  of  the  root  system  especially  on  deep- 
rooted  plants  like  alfalfa,  often  a  large  mass  of  them  are 
found  around  the  top  of  the  tap  root.  The  arrangement 
is  characteristic  with  some  plants  like  the  lupine  on 
which  the  tubercles  grow  as  bunches  on  the  main  root. 

Conditions  for  formation.  It  has  been  found  that 
certain  conditions  are  favorable  for  the  production  of 
the  nodules.  The  soil  must  be  well  aerated  and  not  acid 
in  reaction.  In  very  rich  soils  the  plant  makes  use  of 
the  same  source  of  nitrogen  as  do  the  grains  and  grasses, 
the  nitrates  of  the  soil,  and  there  is  a  tendency  for  the 
nodules  not  to  develop  in  such  numbers  as  on  a  poorer 
soil  where  the  plant  can  not  obtain  sufficient  nitrogen 
from  the  soil,  but  in  order  to  make  a  good  growth  must 
get  some  nitrogen  from  the  air. 

Soil  inoculation.  As  was  previously  stated  unless 
the  plant  has  tubercles  on  the  roots  no  nitrogen  can  be 
fixed  and  the  plant  will  leave  the  soil  poorer  in  nitrogen. 
If  the  legume  is  to  be  a  benefit  to  the  soil,  the  tubercles 
must  be  present.  "While  certain  of  the  bacteria  are  pres- 
ent in  every  soil,  the  kind1  that  will  form  nodules  on 
a  new  kind  of  legume  may  or  may  not  be  in  the  soil.  If 
they  are  not  there,  the  soil  must  be  inoculated.  This  can 
be  done  most  successfully  by  transferring  a  little  soil 
from  a  field  on  which  the  particular  legume  has  grown 
and  on  the  roots  of  which  there  were  an  abundance  of 
nodules.  This  soil  may  be  broadcasted  over  the  field  to 
be  inoculated  or  the  sifted  soil  may  be  applied  with  a 
drill.  Especial  precautions  should  be  taken  to  see  that  the 
higher  parts  of  the  field  are  inoculated  for  these  can  not 


Fixation  of  Nitrogen.  20& 

become  infected  by  surface  drainage  as  can  the  lower 
areas. 

The  disadvantages  connected  with  the  use  of  soil  as  an 
inoculating  agent,  such  as  the  expense,  and  the  introduc- 
tion of  plant  diseases,  has  led  to  the  introduction  of  pure 
cultures  of  the  different  kinds  of  nodule-forming  bacteria 
for  the  inoculation  of  the  soil  or  the  seed.  These  cultures- 
have  been  used  for  many  years  but  have  never  been  as 
successful  as  it  was  hoped  they  would  be.  At  times  the 
inoculated  plants  would  show  an  abundance  of  nodules, 
again  none  could  be  found.  This  uncertainty  of  the  re- 
sult makes  the  use  of  the  pure  cultures  inadvisable  where 
soil  can  be  procured. 

Pure  cultures  of  the  legume  bacteria  are  sent  out  by 
the  U.  S.  Department  of  Agriculture ;  also  by  a  number 
of  the  Experiment  Stations.  These  cultures  are  prepared 
and  sold  by  a  number  of  commercial  laboratories.  They 
are  prepared  for  use  in  various  ways.  In  some  cases 
the  inoculating  material  is  simply  added  to  water  and 
sprinkled  on  the  seed;  in  others  a  culture  is  made  by 
preparing  a  solution  of  the  necessary  food  substances 
which  are  sent  with  the  pure  culture.  The  usual  method 
of  using  the  cultures  is  to  mix  the  same  with  water  and  to 
sprinkle  the  seed  with  it.  The  moistened  seed  is  dried  in 
the  shade  to  protect  the  bacteria  from  the  injurious  ef- 
fect of  sunlight  and  planted  as  soon  as  possible. 

The  inoculation  of  the  soil  should  be  made  whenever  a 
new  legume  is  to  be  grown,  when  a  previous  crop  has 
shown  no  nodules,  or  where  the  nodules  were  few  and 
seemed  to  have  no  effect  on  the  plant.  The  inoculation 
need  not  be  made  when  the  same  plant  has  been  previ- 
ously grown  on  the  field  and  has  shown  tubercles.  With 
many  legumes  the  seed  is  likely  to  be  infected  with  the 


204  Agricultural  Bacteriology. 

nodule-forming  bacteria  and  even  though  no  inoculation 
is  made  some  nodules  will  appear.  If  the  same  legume 
is  then  grown  on  the  field  in  a  subsequent  year,  an  abund- 
ant supply  of  nodules  will  be  produced  as  the  bacteria 
will  persist  in  the  soil  for  a  number  of  years. 

A  large  amount  of  nitrogen  is  removed  from  the  soil  in 
-any  leguminous  crop  but  where  the  nodules  are  abundant 
and  much  nitrogen  has  been  fixed  from  the  air,  the  soil 
is  left  richer  than  before  because  the  nodules  and  roots 
of  the  legumes  are  exceedingly  rich  in  nitrogen.  As 
these  tissues  decay,  the  nitrogen  is  changed  to  a  form  in 
which  it  can  be  used  by  other  kinds  of  plants.  In  this 
way  the  legume  has  a  favorable  effect  on  subsequent  crops. 
The  leguminous  plants  under  all  circumstances  tend  to 
deplete  the  soil  of  phosphorous  and  potassium  in  the  same 
manner  as  all  other  plants. 

Effect  of  nodules  on  composition  of  the  plant.    The 

presence  of  the  increased  nitrogen  supply  derived  from 
the  nodules  affects  materially  the  chemical  composition 
of  the  plant.  Plants  which  have  nodules  on  their  roots 
are  found  to  contain  a  considerable  larger  per  cent  of 
protein  than  plants  devoid  of  the  nodules.  The  feeding 
value  of  the  former  is > consequently  much  greater. 

Nitrogen  fixation  by  bacteria  without  the  aid  of 
plants.  With  those  forms  of  bacteria  that  form  the 
nodules  on  leguminous  plants,  no  fixation  of  nitrogen  is 
supposed  to  take  place,  except  in  the  nodules  of  the  plant. 
The  bacteria  are  known  to  exist  in  the  soil  for  a  number 
of  years  even  though  no  leguminous  plants  are  grown  on 
the  field.  It  is  thus  evident  that  the  bacteria  must  be 
able  to  grow  in  the  soil  outside  of  the  plant. 

There  are  found  widely  distributed  in  the  soil,  other 


Fixation  of  Nitrogen.  205 

kinds  of  bacteria  that  are  able  to  fix  the  free  nitrogen  of 
the  air  and  build  it  up  into  their  own  protoplasm.  They 
are  able  to  grow  in  media  that  contain  no  nitrogen  and 
must  then  satisfy  their  needs  from  the  nitrogen  supply 
of  the  air.  It  is  supposed  that  a  large  part  of  the  nitro- 
gen of  the  soil  has  been  brought  into  combination  by  the 
action  of  these  bacteria.  It  has  been  shown  that  a  soil 
on  which  no  plants  of  any  kind  are  growing  will  increase 
in  its  content  of  nitrogen,  and  it  is  believed  that  it  is. 
largely  due  to  these  germs.  Unlike  the  nodule-forming 
bacteria,  the  fixation  of  nitrogen  by  this  second  class, 
known  as  the  azotobacter  group,  can  go  on  independent 
of  the  kind  of  plants  that  may  happen  to  be  growing  in 
the  field. 

It  is  important  to  know  the  conditions  that  favor  the 
growth  of  these  nitrogen-fixing  bacteria.  They  are 
aerobic ; .  hence,  grow  best  in  a  soil  that  is  thoroughly 
aerated,  stirred  and  drained.  They  demand  a  supply  of 
available  potash  and  phosphorus  as  well  as  organic  mat- 
ter from  which  they  derive  the  energy  necessary  for  the 
fixation  of  the  nitrogen.  In  the  laboratory  the  largest 
amount  of  nitrogen  is  fixed  in  a  food  medium  that  con- 
tains a  sugar  such  as  cane  sugar  or  mannit.  In  the  soil, 
it  is  believed  that  they  use  the  different  carbohydrates 
contained  in  the  plant  residues  that  are  added  in  the 
roots  of  crops,  in  the  green  crop  plowed  under,  or  in  the 
manure. 

In  the  case  of  uncultivated  land,  the  greater  part  jf 
the  annual  crop  falls  onto  the  ground,  and  undergoes  de- 
composition. The  nitrogen-fixing  bacteria  are  thus  fur- 
nished with  suitable  food  to  accomplish  the  fixation  of 
nitrogen,  and  the  content  of  the  soil  in  this  important 


206  Agricultural  Bacteriology. 

element  slowly  increases.  On  cultivated  fields  this  crop 
of  organic  matter  is  largely  removed,  so  that  conditions 
are  not  so  favorable  for  the  development  of  this  type  of 
life.  As  a  consequence  less  nitrogen  is  brought  into  com- 
bination, and  a  more  rapid  depletion  of  the  total  nitro- 
gen supply  of  the  soil  takes  place. 


CHAPTER  XXIII. 
BACTERIA  IN  MANURES. 

The  waste  products  of  the  animal  body  are  elimi- 
nated largely  in  the  urine  and  feces.  The  latter  consist, 
in  the  main,  of  the  undigested  and  indigestible  parts  of 
the  food;  the  urine  contains  the  waste  of  all  activities 
of  the  different  tissues  of  the  body.  The  changes  that 
the  food  undergoes  in  the  body  of  the  animal,  must  be 
looked  upon  as  a  part  of  the  complex  process  by  which 
organic  matter  is  again  rendered  available  to  the  green 
plant.  The  material  that  is  eliminated  from  the  animal 
is  much  more  easily  decomposed  by  bacterical  action  than 
is  the  food  consumed.  That  which  comes  from  the  in- 
testinal tract  is  already  well  advanced  in  the  series  of 
changes  that  occur  in  the  transformation  of  the  organic 
matter  into  stable  form.  It  is  interesting  to  know  that  the 
work  of  the  bacteria  begins  in  the  body  of  the  animal,  and 
that  their  action  on  certain  parts  of  the  food  is  of  value  to 
the  animal,  enabling  it  to  make  use  of  parts  of  the  food 
that  without  their  aid  would  be  impossible. 

As  previously  noted,  the  alimentary  tract  of  animals 
is  to  be  considered  as  one  of  the  natural  homes  of  the 
bacteria.  Food  is  abundant,  while  temperature  and 
moisture  conditions  are  favorable  for  rapid  growth. 
Over  one-fourth  of  the  solid  matter  in  human  feces  con- 
sists of  bacterial  cells.  In  the  feces  of  the  domestic  ani- 
mal, the  proportion  of  bacteria  is  much  less  because  of 
the  nature  of  the  food.  ^Millions  of  bacteria  exist  in 
every  gram  of  the  manure. 


208  Agricultural  Bacteriology. 

Digestion  of  cellulose.  Coarse  fodder,  such  as  hayr 
straw,  or  corn  fodder  contains  a  large  proportion  of  crude 
fiber  or  cellulose.  It  is  known  that  different  kinds  of 
animals  can  digest  this  class  of  substances  to  a  varying 
extent.  In  the  different  digestive  juices  of  the  body  have 
been  found  enzymes  that  can  attack  carbohydrates,  fats 
and  proteins.  None  have  been  discovered  that  have  any 
action  on  cellulose.  There  are  in  the  feces  of  animals, 
bacteria  that  can  digest  the  cellulose,  changing  it  to  com- 
pounds that  can  be  used  by  the  animal.  It  is  asserted 
that  ruminating  animals  can  digest  75  per  cent  of  the 
cellulose  in  their  food,  and  the  horse  50  per  cent.  Dogs 
and  the  strictly  carnivorous  animals  cannot  utilize  this 
material  at  all.  In  the  case  of  the  ruminating  animals 
the  food  remains  in  the  body  for  a  long  time,  as  for  in- 
stance, in  the  cow  for  six  or  seven  days,  and  with  sheep 
possibly  a  still  longer  time.  There  is  thus  opportunity 
for  extended  bacterial  action  in  such  a  favorable  environ- 
ment. In  man  the  food  passes  through  the  body  in  a 
much  shorter  time,  and  there  is  not  the  opportunity  for 
the  bacteria  to  attack  the  cellulose. 

It  is  very  probable  that  the  bacteria  of  the  intestinal 
tract  are  necessary  to  the  well-being  of  all  kinds  of  ani- 
mals. At  the  time  of  birth,  the  intestines  are  free  from 
bacteria  but  within  a  short  time,  less  than  a  day,  the  bac- 
teria have  invaded  the  entire  tract.  Definite  kinds  'of 
bacteria  are  found  to  occur.  When  these  are  replaced 
by  other  forms,  the  animal  is  quite  likely  to  suffer. 

Composition  of  barnyard  manure.  Manure  is  made 
up  of  the  solid  and  liquid  excreta  of  the  different  kinds 
of  animals  kept  on  the  farm  and  of  the  litter  used  in  the 
stables.  It  thus  contains  all  of  the  compounds  found  in 
the  plant,  and  will  undergo,  in  the  main',  the  same  set  of 


Bacteria  in  Manures.  209 

changes  that  the  plant  tissue  does  in  the  soil.  As  has 
been  previously  stated,  it  is  of  the  greatest  advantage  to 
the  farmer  to  return  to  the  soil  as  large  a  part  of  the  ma- 
terial removed  in  the  crop  as  possible.  This  is  true  not 
only  for  the  mineral  ingredients  of  the  soil,  as  potassium 
and  phosphorus,  but  also  for  the  organic  matter.  The 
problem  of  the  farmer  is  to  handle  all  manures  made  on 
the  farm  in  such  a  way  that  the  least  loss  may  occur. 

Decomposition  of  manure.  Manure  when  placed  in 
piles  rapidly  decomposes  under  the  action  of  micro-or- 
ganisms, continuing  as  it  were,  the  changes  inaugurated 
in  the  intestinal  tract.  The  bacteria  voided  with  the  ex^ 
creta  serve  to  inoculate  the  bedding  or  litter  used.  The 
bacteria  decompose  the  organic  matter  with  the  result 
that  in  a  well-rotted  manure,  but  little  trace  of  the  ma- 
terial used  as  bedding  can  be  found. 

Nitrogenous  compounds.  Stable  manure  contains 
various  nitrogen-containing  compounds  that  are  found  in 
the  plant.  These  undergo  a  process  of  ammonification, 
due  to  the  action  of  the  same  kinds  of  bacteria  that  are 
responsible  for  similar  changes  in  the  soil.  A  part  of  the 
nitrogen  that  is  used  in  the  cell  processes  of  the  animal 
is  eliminated  in  the  urine  in  the  form  of  urea,  uric  acid, 
and  hippuric  acid.  These  substances  are  converted  into 
ammonia  salts.  In  the  summer  the  odor  of  ammonia  is 
often  noticeable  in  horse  manure,  due  to  the  decomposi- 
tion of  the  nitrogenous  compounds  in  the  urine.  The  am- 
monification of  the  nitrogen  in  the  solid  manure  and  in 
the  litter  is  less  rapid.  As  ammonia  is  readily  soluble 
and  is  also  volatile,  it  follows  that  where  fermentation  is 
rapid  much  of  this  valuable  fertilizing  ingredient  is  lost 
in  the  leachings  from  the  pile  or  passes  off  into  the  air. 


210  Agricultural  Bacteriology. 

Much  of  this  loss  can  be  prevented  by  the  use  of  proper 
methods  which  will  be  described  later. 

In  the  manure  heap  the  ammonia  is  not  changed  into 
nitrates  as  it  is  in  the  soil  for  the  conditions  are  not  fav- 
orable for  the  nitrifying  bacteria.  Organic  matter  is  too 
abundant  and  oxygen  is  also  lacking  except  in  the  outer 
layers  of  the  pile.  If  the  manure  is  allowed  to  stand, 
especially  if  it  has  been  mixed  with  earth,  until  it  is  com- 
pletely decomposed,  a  small  amount  of  nitrate  will  be 
found.  Since  no  nitrates  are  formed,  denitrification  can- 
not take  place. 

Cellulose  decomposition.  The  decomposition  of  the 
cellulose  begun  in  the  animal  is  continued  in  the  manure 
pile  by  the  same  kind  of  bacteria  as  in  the  body  of  the 
animal.  The  starches  and  sugars,  etc.,  are  also  readily 
fermented  by  micro-organisms,  and  carbon  dioxide, 
water,  hydrogen,  and  organic  acids  are  formed. 

Losses  from  manure.  It  is  impossible  to  return  to 
the  soil  all  of  the  organic  matter  removed  in  the  crop, 
even  though  the  entire  crop  is  fed  to  farm  animals  and 
the  manure  carefully  handled.  In  the  respiration  of  ani- 
mals a  large  amount  of  carbon  is  eliminated  from  the 
body ;  this  was  taken^  in  with  the  food.  Oxygen  and  hy- 
drogen in  the  form  of  water  are  given  off  as  respiratory 
products  and  in  the  perspiration.  The  nitrogen  and 
mineral  ingredients  are  eliminated  in  the  same  amounts 
as  are  contained  in  the  food  consumed,  except  for  the 
quantity  retained  in  the  tissues  of  the  animal.  This  is 
of  course  much  more,  in  the  case  of  a  growing  than  a  ma- 
ture animal. 

In  the  decomposition  processes  in  the  manure  pile,  the 
organic  matter  is  destroyed,  which  is  in  itself  a  loss  to 
the  soil,  since  if  applied  to  the  land,  it  would  have  fur- 


Bacteria  in  Manures.  211 

nished  food  for  bacteria,  especially  the  nitrogen-fixing 
ones,  and  have  added  to  the  humus  content  of  the  soil. 
J  t  is  now  realized  that  the  value  of  manure  is  not  deter- 
mined alone  by  the  amount  of  potassium,  phosphorus, 
and  nitrogen  it  contains,  but  the  organic  matter  itself 
exerts  a  most  important  effect.  Market  gardeners  find 
it  advantageous  to  pay  more  for  manure  than  the  fertiliz- 
ing ingredients  alone  would  cost  in  the  form  of  commer- 
cial fertilizers.  For  most  soils  the  greater  the  amount  of 
organic  matter  that  can  be  returned  the  better  for  the 
soil.  The  practice  of  hauling  manure  directly  to  the  field 
from  the  stable  is  probably  the  most  successful  means  of 
conserving  its  value. 

If  very  large  amounts  of  manure  are  to  be  applied,  as 
in  market  gardening,  unrotted  manure  cannot  be  used  on 
account  of  its  injurious  effect  on  the  crop.  The  amounts 
usually  applied  in  farm  practice  have  no  injurious  effect. 

The  potassium  and  phosphorus  of  the  manure  are 
changed  to  soluble  form  in  the  decomposition  processes. 
These  can  be  lost  from  the  manure  only  through  the 
leaching  of  the  pile.  The  largest  loss  is  liable  to  occur  in 
the  case  of  nitrogen  when  ammonia  is  freely  formed.  In 
order  to  prevent  the  loss  in  the  latter  form,  materials 
such  as  gypsum,  kainit,  sulphuric  acid,  and  peat,  that 
were  supposed  to  fix  the  ammonia,  were  formerly  em- 
ployed. It  is  now  recognized  that  the  loss  prevented  by 
their  use  is  very  small,  and  they  are  no  longer  used  to 
any  extent. 

Hot  and  cold  manures.  Horse  and  sheep  manures 
are  called  hot  manures  because  if  placed  in  a  pile  they 
heat  or  fire  fang.  Cow  and  hog  manure  are  cold  ma- 
nrires.  During  their  decomposition  enough  heat  is 
evolved  to  keep  them  from  freezing  in  quite  severe 


212  Agricultural  Bacteriology. 

weather,  but  they  never  fire  fang.  This  difference  is 
primarily  due  to  the  physical  condition  of  the  manure 
and  to  its  water  content.  The  horse  manure  is  dry  and 
open,  allowing  the  air  to  penetrate  into  the  pile,  while 
cow  manure,  even  when  large  amounts  of  bedding  are 
used,  is  of  such  a  physical  texture  that  air  cannot  enter. 
The  large  amount  of  air  in  the  horse  manure  permits  the 
growth  of  aerobic  bacteria  and  molds.  The  heat  evolved 
by  their  respiration  is  great  and  the  decomposition  they 
produce  very  complete.  The  organic  matter  is  practi- 
cally burned,  the  carbon,  hydrogen,  and  nitrogen  pass- 
ing into  the  air.  Where  decomposition  occurs  under  an- 
aerobic conditions  the  process  is  much  slower  and  less 
complete.  If  a  pile  of  horse  manure  is  well  packed,  so 
as  to  exclude  the  air,  the  usual  aerobic  fermentation  will 
not  occur,  but  will  be  supplanted  by  anaerobic  action. 
In  such  a  case  the  loss  of  nitrogen  and  organic  matter 
will  be  much  less. 

In  handling  any  manure,  the  activity  of  aerobic  organ- 
isms should  be  excluded  as  far  as  possible  by  piling  the 
manure  in  large  compact  piles  of  considerable  depth.  If 
the  man  are  is  allowed  to  accumulate  in  the  stalls  or  feed- 
ing sheds  in  which  the  animals  run  loose,  the  loss  will  be 
reduced  to  the  minimum,  since  the  constant  tramping  of 
the  animals  excludes  the  air,  and  the  manure  is  protected 
from  leaching. 

If  the  manure  is  hauled  directly  to  the  field  from  the 
stall  the  decomposition  goes  on  to  some  extent  on  the  sur- 
face, but  the  soluble  products  formed  pass  into  the  soil. 
There  may  be  some  loss  of  nitrogen  as  ammonia,  but  it  is 
certain  that  the  losses  are  much  smaller  than  when  the 
manure  is  allowed  to  rot  in  piles.  If  it  is  not  possible  to 
apply  it  directly,  the  piles  should  be  thoroughly  packed 


Bacteria  in  Manures.  213 

and,  if  under  cover,  should  be  kept  moist.  The  average 
difference  in  temperature  between  a  loose  pile  of  cow 
manure  from  which  the  water  was  allowed  to  drain,  and 
one  placed  in  a  tight  concrete  pit  and  well  packed,  was 
98°  F.  for  one  month  after  the  manures  were  placed  in 
the  pits.  Heat  in  the  manure  pile  indicates  a  combus- 
tion of  organic  matter  as  much  as  in  a  furnace.  The  loss 
from  the  loose  pile  amounted  to  53  per  cent  of  the  or- 
ganic matter  and  34  per  cent  of  the  nitrogen ;  in  the  com- 
pacted pile  the  losses  were  28  and  15  per  cent  respec- 
tively. 


CHAPTER  XXIV. 
WATER  SUPPLY  AND  SEWAGE  DISPOSAL. 

An  abundant  supply  of  pure  and  healthful  water  is  one 
of  the  necessities  of  modern  life,  whether  in  the  city  or  on 
the  farm.  In  the  city,  the  home  is  provided  with  this  ne- 
cessity through  the  action  of  the  municipality ;  the  indi- 
vidual citizen  does  not  have  to  concern  himself  with  the 
question  as  to  the  source  and  quality  of  the  water  sup- 
plied, while  on  the  farm  the  problem  of  obtaining  a  plen- 
tiful supply  of  water  fitted  for  household  purposes  is  an 
individual  one,  and  one  that  is  frequently  neglected,  al- 
though it  means  so  much  to  the  comfort  and  health  of 
the  farm  home. 

Modern  cities  are  spending  immense  sums  of  money  in 
securing  safe  and  adequate  water  supplies  and  in  pro^ 
tecting  them  from  pollution.  The  farmer  should  use  the 
same  foresight  and  the  cost  for  supplying  the  farm  home 
with  good  water  will  be  no  greater  than  must  be  paid  by 
the  home  in  the  city. 

Relation  of  water  to  disease.  A  number  of  transmis- 
sible diseases  may  be  carried  from  one  person  to  another 
through  the  medium  of  the  drinking  water.  The  most 
important  of  these  are  typhoid  fever  and  cholera.  The 
former,  a  world-wide  disease,  the  latter  one  that  is  not 
found  at  present  in  America  and  Western  Europe.  The 
reason  these  diseases  are  often  spread  by  means  of  water 
is  to  be  found  in  the  fact  that  the  bacteria  are  given  off 
from  the  body  in  the  urine  and  feces  and  as  great  care- 


Water  Supply  and  Sewage  Disposal.  215 

lessness  often  prevails  in  the  matter  of  disposal  of  house- 
hold sewage,  the  water  supply  becomes  contaminated. 
The  sewage  of  a  city  may  be  discharged  into  a  river,  from 
which  another  city  a  few  miles  further  down  draws  its 
water  for  household  use.  A  city  may  discharge  its  sew- 
age into  a  lake  and  from  the  same  source  draw  its  water 
supply,  as  is  the  case  with  nearly  all  the  cities  on  the 
Great  Lakes.  Under  such  conditions  more  or  less  of  the 
sewage  is  certain  to  enter  the  water  mains.  As  stated  in 
the  discussion  on  the  relation  of  milk  to  transmissible  dis- 
eases, there  are  people  who  have  recovered  from  typhoid 
fever  and  who  continue  to  harbor  in  and  give  off  from 
their  bodies  the  disease-producing  organisms.  These 
people  are  supposed  to  be  the  means  by  which  the  disease 
maintains  its  presence  in  the  community,  no  matter  how 
much  care  may  be  used  in  the  disinfection  of  the  dis- 
charges of  persons  known  to  be  suffering  from  typhoid 
fever.  Cities  now  realize  that  it  is  economy  for  them  to- 
protect  themselves  by  securing  their  water  supply  from 
sources  known  to  be  free  from  pollution  with  sewage,  or 
through  purification  by  the  proper  filtration  of  water 
from  suspected  sources. 

The  farm  home  should  likewise  be  insured  against  ty- 
phoid fever  through  the  protection  of  its  water  supply 
from  sewage  pollution.  It  is  frequently  thought  that 
typhoid  fever  is  an  urban  disease,  but  as  a  matter  of  fact 
it  is  more  prevalent  in  the  country.  The  city  home  is  ex- 
posed to  infection  by  means  of  the  water  from  many  other 
homes  in  which  typhoid  may  be  present,  while  the  farm 
home  is  not  related  in  so  direct  a  manner  with  other 
places  in  which  the  disease  may  be  present.  There,  are, 
however,  abundant  ways  in  which  the  disease  may  be 
brought  on  to  the  farm. 


216 


Agricultural  Bacteriology. 


Relation  of  water  to  soil.  As  was  previously  stated 
the  upper  layers  of  the  soil  are  rich  in  germ  life.  The 
drainage  water  from  such  places  will  be  teeming  with 
bacteria.  The  shallow  dug  well,  loosely  bricked  up,  is 
filled  during  the  wet  seasons  with  water  coming  from  the 
upper  layers  of  the  soil.  If  material  containing  disease- 
producing  bacteria  is  placed  on  the  ground  near  the  well, 
as  in  a  privy  vault,  the  bacteria  may  be  carried  by  the 
percolating  water  into  the  well.  The  distance  between 
the  vault  and  the  well  that  is  required  to  prevent  pollu- 


CESS  POOL 


FIG.  21. — POLLUTION  OF  A  WELL. 

The  well  water  may  be  polluted  from  a  cess  pool  or 
vault  by  the  percolation  of  the  ground  water  into 
the  well.  (After  Harrington.) 

tion  of  the  well  can  not  be  stated  in  definite  terms  as  it 
will  depend  on  the  nature  of  the  soil,  whether  it  is  close 
and  dense  as  in  a  clay  soil,  whether  it  is  porous,  as  a  sandy 
soil,  or  whether  the  percolating  water  may  form  channels 
in  it,  as  in  lime  stone.  The  distance  that  may  be  tra- 
versed by  bacteria  in  the  underground  water  also  de- 
pends on  the  slope  of  the  underlying  rocks.  A  well  on 
Tiigher  ground  than  a  privy  is  not  necessarily  protected 
from  pollution. 


Water  Supply  and  Sewage  Disposal.  217 

As  the  water  percolates  through  the  soil,  the  bacteria 
are  removed  until  at  a  varying  depth  beneath  the  surface 
no  organisms  are  found.  The  water  that  enters  a  well 
from  the  lower  layers  of  the  soil  may  be  free  from  bac- 
teria. Such  a  supply  is  the  most  desirable  if  it  can  be 
pumped  from  the  well  in  the  same  condition  as  when  it 
entered.  In  order  to  obtain  the  water  in  this  condition, 
the  well  must  be  protected  from  all  surface  drainage.  It 
is  very  difficult  to  obtain  this  condition  except  in  the 
case  of  a  drilled  well  which  is  cased  with  a  threaded  iron 
pipe,  and  which  is  protected  at  the  top  so  that  no  water 
can  enter  the  casing.  A  dug  well,  even  if  provided  with 
a  tight  wall  to  a  considerable  depth,  is  likely  to  receive 
more  or  less  surface  water  and  hence  is  liable  to  pollu- 
tion. 

The  well  should  be  so  arranged  at  the  surface  that  no 
surface  water,  or  water  that  is  pumped  onto  the  curb  can 
enter  the  well,  for  material  containing  disease-producing 
bacteria  may  be  brought  on  to  the  curb  and  in  this  way 
pollute  the  water.  The  dug  well,  so  common  in  the  older 
sections  of  the  country,  is  a  menace  and  should  be  re- 
placed by  the  safer  drilled  well.  The  old-fashioned  well 
with  bucket  and  sweep,  which  is  so  often  regarded  with 
sentiment,  is  the  most  dangerous  type  of  well,  even 
though  the  water  is  clear  and  sparkling. 

The  water  of  a  well  that  receives  surface  drainage  is 
not  harmful  at  all  times,  but  it  may  become  so  at  any 
time.  The  conditions  needed  to  produce  disease  are  all 
present  except  one,  viz,  the  deposition  of  material  that 
contains  disease-producing  bacteria  within  the  zone  from 
which  the  water  percolates  into  the  well.  This  essential 
condition  may  not  be  present  for  years,  but  at  last  it  is 


218  Agricultural  Bacteriology. 

introduced  and  an  outbreak  of  typhoid  fever  occurs  in« 
the  family. 

On  the  diary  farm,  as  previously  mentioned,  an  oppor- 
tunity is  offered  for  the  farther  spread  of  the  disease  by 
means  of  the  milk  infected  from  the  water  or  in  some 
other  way.  The  wise  course  to  follow  is  to  supply  thd 
home  with  water  that  is  so  protected  that  it  cannot  be  the 
cause  of  disease,  even  if  material  containing  typhoid  bac- 
teria is  deposited  near  the  well.  This  demands  a  well 
into  which  no  water  can  enter  except  that  which  has  per- 
colated through  a  sufficient  bed  of  soil  to  insure  its  free- 
dom from  all  harmful  bacteria.  This  demands  again  the 
positive  exclusion  of  water  from  the  upper  layers  of  the 
soil  by  the  use  of  a  non-porous  wall,  preferably  an  iron  * 
pipe,  and  the  protection  of  the  well  at  the  surface. 

Springs  are  the  outlet  of  under-ground  streams. 
Spring  water  is  free  from  bacteria  as  it  flows  from  the 
ground  and  is,  of  course,  an  excellent  water  for  house- 
hold use,  but  there  is  often  danger  of  surface  pollution 
entering  the  basin  of  the  spring,  unless  it  is  carefully 
protected. 

The  first  consideration  in  obtaining  water  for  the  home 
should  be  to  secure  a  safe  supply  that  is  thoroughly  pro- 
tected from  all  possible  pollution  with  disease-producing 
bacteria.  An  adequate  supply  is  also  a  consideration  of 
great  importance  in  order  that  the  farm  home  may  be 
provided  with  the  modern  conveniences.  These  so-called 
"modern  conveniences"  such  as  water  carriage  for  dis- 
posal of  sewage,  drinking  water  under  pressure  and  also 
hot  and  cold  water  supplies  for  lavatory,  laundry,  and 
bath  have  been  regarded  as  obtainable  only  in  the  city, 
and  yet  all  of  these  sanitary  arrangements  are  readily 
secured  if  an  adequate  water  supply  is  available. 


Water  Supply  and  Seivage  Disposal.  219 

Sewage  disposal.  The  disposal  of  house  sewage  by 
water  carriage  is  not  only  a  matter  of  great  convenience 
but  a  hygienic  necessity.  Through  the  use  of  the  ordi- 
nary open  vault  there  is  not  only  opportunity  for  the  pol- 
lution of  the  well  water  but  the  disease-producing  bac- 
teria may  be  carried  from  the  privy  vault  to  the  kitchen, 
the  milk  room,  and  elsewhere  by  means  of  the  common 
house  fly.  If  the  sewage  can  be  disposed  of  in  a  conven- 
ient way  and  yet  avoid  the  danger  of  pollution  of  water 
and  food  much  will  be  done  for  the  comfort  and  health  of 
the  home. 

Cities  that  are  located  on  a  body  of  water  often  dis- 
charge their  sewage  into  the  river  or  lake.  Others  less- 
favorably  located  find  it  necessary  to  dispose  of  the 
wastes  in  other  ways,  utilizing  different  methods  of  puri- 
fication that  shall  render  the  sewage  comparatively  harm- 
less. Most  of  these  methods  of  purification  depend  on 
the  work  of  bacteria.  The  sewage  contains  organic  mat- 
ter of  various  kinds,  which  will  be  decomposed  in  the 
same  manner  as  has  been  shown  to  occur  in  the  soil.  The 
final  products  will  be  harmless,  and  in  the  process  of  de- 
composition the  disease-producing  bacteria  will  be  de- 
stroyed. 

The  methods  of  sewage  purification  seek  to  establish 
conditions  favorable :  (1)  for  the  growth  of  anaerobic  bac- 
teria that  shall  render  soluble  all  solid  matter  contained 
in  the  sewage  just  as  the  solids  are  made  soluble  in  the 
soil ;  (2)  for  the  development  of  the  aerobic  bacteria  that 
shall  complete  the  work  of  decomposition,  and  the  nitri- 
fying bacteria  that  change  the  ammonia  to  nitric  acid. 
Modifications  of  the  types  of  plants  used  by  cities  in 
the  disposal  of  large  quantities  of  sewage  can  be  used  on 
the  farm  for  the  safe  and  convenient  disposal  of  the 


220  Agricultural  Bacteriology. 

house  wastes.  The  cost  of  such  a  plant  need  not  be  more 
than  the  city  home  must  pay  toward  the  construction  of 
the  sewers  of  the  city. 

The  conditions  that  exist  on  the  farms  differ  so  greatly 
that  it  is  impossible  to  give  a  detailed  description  of  a 
disposal  plant  that  will  answer  the  needs  of  all  farms. 
In  the  following  description,  the  essential  conditions  thai 
must  be  established  in  order  to  have  a  successful  plant 
will  be  given. 

The  house  should  be  provided  with  a  pressure  tank, 
either  in  the  elevated  form,  or  one  in  which  the  pressure 
is  maintained  by  compressed  air,  so  that  flushing  arrange- 
ments can  be  used  in  the  water  closets. 

Septic  tanks.  The  sewage  passes  from  the  house 
drain  into  a  tank  in  which  it  is  allowed  to  remain  for  sev- 
eral days.  The  tank  can  best  be  made  of  concrete.  It 
should  be  placed  beneath  the  ground  so  as  to  avoid  freez- 
ing. It  should  be  large  enough  to  hold  the  accumula- 
tions of  several  days,  since  it  is  necessary  that  time  be 
given  for  the  bacteria  to  decompose  the  solid  matter.  A 
period  of  four  days  is  sufficient,  although  a  longer  time 
will  have  advantages.  The  amount  of  household  sewage 
will  not  exceed  a  barrel  per  day  per  person  on  the  aver- 
age farm.  Thus  a  tank  holding  thirty  to  forty  barrels 
will  suffice  for  a  family  of  six  persons. 

The  sewage  as  it  passes  into  the  septic  tank  contains 
much  organic  matter  in  solution  and  is  in  condition  to 
serve  as  bacterial  food.  The  solid  matter  of  the  sewage 
sinks  to  the  bottom  of  the  tank  and  is  rendered  soluble 
by  the  continued  bacterial  action.  On  the  surface  of  the 
sewage  a  scum  collects  which  shuts  out  all  air  and  gives 
favorable  conditions  for  the  growth  of  anaerobic  bacteria. 
The  sewage  as  it  flows  from  the  tank  after  four  or  five 


Water  Supply  and  Sewage  Disposal.  221 

days  exposure  is  a  turbid  liquid  with  a  disagreeable  odor. 
The  bacterial  action  is  so  complete  that  the  solid  organic 
matter  is  wholly  destroyed  and  scarcely  any  sediment 
collects  in  the  tank ;  hence  it  need  be  emptied  and  cleaned 
only  at  intervals  of  several  years.  The  tank  must  be  so 
arranged  that  a  quantity  of  sewage  can  be  discharged 
from  it  at  intervals  rather  than  constantly  as  is  the  case 
with  the  sewage  flowing  into  the  tank. 

The  sewage  should  remain  in  the  tank  for  a  sufficient 
length  of  time  so  that  it  will  no  longer  putrefy.  If  this 
is  accomplished,  the  farther  steps  in  purification  and  dis- 
posal can  often  be  very  simple.  If  the  septic  tank  is  so 
situated  that  a  drain  can  be  laid  which  shall  discharge 
onto  the  surface  of  a  field  that  has  some  fall  at  a  distance 
from  the  house,  the  sewage  can  be  discharged  onto  the 
surface  of  the  soil.  Since  the  sewage  contains  no  solid 
matter  it  sinks  rapidly  into  the  soil,  where  the  purifica- 
tion is  completed.  This  arrangement  can  best  be  used 
on  a  sandy  or  loose  soil.  The  drain  should  empty  into 
open  furrows.  Since  the  tank  is  arranged  so  that  the 
sewage  can  be  discharged  at  intervals  the  soil  has  an  op- 
portunity to  become  aerated  between  the  periods  of  dis- 
charge. This  avoids  keeping  the  soil  saturated  with 
moisture  which  of  course  would  be  detrimental  to  nitrifi- 
cation. A  preferable  process  is  to  discharge  the  sewage 
from  the  tank  into  drains  of  ordinary  tile  laid  with  open 
joints.  The  sewage  as  it  flows  from  the  tank  at  intervals 
fills  the  tile  and  gradually  percolates  into  the  soil 
through  the  open  joints.  On  account  of  the  intermittent 
discharge  it  has  time  to  drain  away  and  thus  favorable 
conditions  for  nitrification  are  maintained.  If  the  sew- 
age flows  into  the  drains  constantly,  it  would  all  seep 
out  through  the  first  few  joints  and  keep  the  soil  water- 


222  Agricultural  Bacteriology. 

logged.  With  the  discharge  at  intervals,  the  entire  line 
of  tile  is  filled  and  no  part  of  the  soil  is  kept  in  a  satu- 
rated condition. 

The  tiles  should  be  laid  18-24  inches  below  the  sur- 
face, the  trench  about  the  tile  should  be  filled  with  cin- 
ders or  gravel  so  that  the  water  may  pass  out  of  the  tiles 
freely.  It  is  not  necessary  to  place  the  tile  below  the 
frost  line,  although  they  will  be  somewhat  disintegrated 
by  freezing  and  the  system  will  have  to  be  dug  up  more 
frequently  than  if  freezing  did  not  occur.  If  the  tile  are 
laid  too  deeply,  the  amount  of  oxygen  is  small  and  nitrifi- 
cation is  retarded.  In  a  loose,  sandy  soil,  the  tile  can 
be  laid  deeper  than  in  a  dense  soil  and  a  much  shorter 
line  of  tile  will  suffice.  By  increasing  the  length  of  the 
tile  drains,  the  system  will  work  in  a  satisfactory  manner 
in  a  close  clay  soil.  The  tile  can  be  laid  beneath  a  cul- 
tivated field  or  beneath  the  lawn  since  they  need  be  re^ 
moved  and  cleaned  only  at  intervals  of  several  years. 

The  essential  parts  of  the  system  are:  (1)  a  supply  of 
water  for  the  flushing  of  closets,  etc. ;  (2)  the  house  so  sit- 
uated that  a  small  amount  of  fall  can  be  had  away  from 
it  in  order  that  the  septic  tank  can  be  emptied  into  the 
drains;  (3)  a  septic  tank  large  enough  to  hold  the  quan- 
tity of  sewage  produced  in  three  or  four  days  so  that 
ample  time  can  be  given  for  decomposition  of  the  solid 
matter;  (4)  a  method  of  discharging  a  quantity  of  sew- 
age at  intervals. 

In  the  accompanying  figure  the  general  arrangement  of 
a  sewage  disposal  plant  is  given.  The  main  drain  enters 
the  septic  tank  below  the  surface  of  the  liquid  so  as  to 
avoid  disturbing  the  scum  on  the  surface  or  the  sediment. 
The*  first  compartment,  the  septic  tank  proper,  should 
hold  at  least  three  days  sewage  and  is  separated  from  the 


Water  Supply  and  Sewage  Disposal. 


223 


second  compartment  by  a  partition  that  does  not  reach 
the  top  of  the  tank.  When  the  first  compartment  is 
filled,  the  sewage  runs  over  the  top  of  the  partition  and 
gradually  fills  the  second  compartment.  In  order  to 
prevent  the  scum  from  passing  into  the  second  compart- 
ment a  baffle  board  is  bolted  to  the  partition  in  such  a 
manner  that  its  top  is  above  the  level  of  the  scum  while 
its  bottom  dips  into  the  liquid.  Some  space  is  left  be- 
tween the  baffle  board  and  the  partition. 


FIG.  22. — A  SEPTIC  TANK. 

A.  drain  from  the  house;  B.  baffle  board  to  keep  the 
scum  (C)  from  passing  into  the  second  compart- 
ment; D.  plug  closing  the  entrance  to  the  drain. 

At  any  desired  time  the  second  compartment  is  emp- 
tied by  pulling  the  plug  which  closes  the  opening  of  the 
drain.  The  entire  contents  of  the  chamber  is  discharged 
into  the  drain  at  once.  The  plug  should  fit  tightly  so  as 
to  prevent  constant  leaking  of  sewage  into  the  drains. 
The  second  compartment  should  be  of  about  the  same 
capacity  as  the  first.  An  overflow  pipe  is  provided  so 
that  if  the  second  compartment  becomes  full,  the  tank 


224  Agricultural  Bacteriology. 

will  not  be  flooded.  The  opening  of  the  overflow  should" 
extend  to  the  surface  and  be  protected  by  a  screen,  thus 
allowing  air  to  pass  in  and  out  of  the  drains. 

The  two  compartments  can  be  made  of  different 
depths  if  desired.  The  first  can  be  increased  in  capacity 
by  increasing  its  depth;  this  also  serves  to  aid  in  main- 
taining a  constant  temperature  in  the  sewage.  The  sec- 
ond division  can  be  of  less  depth,  thus  aiding  in  obtain- 
ing .the  necessary  fall  where  the  slope  of  the  ground  is 
slight. 

Such  a  disposal  plant  will  work  for  a  number  of  years 
with  no  attention  except  the  emptying  of  the  second  com- 
partment at  regular  intervals.  If  the  drains  run  be- 
iieath  the  garden,  a  constant  supply  of  moisture  and  of 
plant  food  is  supplied  to  the  plants. 


SECTION  V. 

FOOD  PRESERVATION  AND  DISEASES  OF 
PLANTS. 


CHAPTER  XXV. 
PRESERVATION  OF  FOODS. 

All  organic  matter  whether  of  plant  or  animal  origin 
is  subject  to  the  attacks  of  living  organisms  which  find 
in  it  favorable  conditions  for  growth.  The  changes  in- 
duced are,  in  the  main,  decomposition  changes  which 
usually  render  the  material  unfit  for  use  as  food  either 
by  human  beings  or  animals.  Food  supplies  that  are  to 
be  kept  for  any  length  of  time  must  be  treated  so  as  to 
prevent  or  retard  the  growth  of  micro-organisms.  This 
can  be  done  in  a  variety  of  ways. 

Drying.  One  of  the  most  common  ways  of  preserv- 
ing organic  matter  is  to  dry  it,  so  that  the  water  content 
is  reduced  to  a  point  where  growth  of  micro-organisms 
in  or  on  the  material  is  impossible.  The  bacteria  can 
grow  only  in  the  presence  of  considerable  amounts  of 
moisture.  Molds  demand  much  less  moisture  for  their 
growth,  hence  many  things  may  be  protected  from  bac- 
terial action  and  still  be  spoiled  by  the  growth  of  molds. 

Fodders  of  all  kinds  are  dried  in  the  field  before  plac- 
ing in  the  barn.  If  hay  or  dried  forage  is  not  thoroughly 
dried,  it  will  heat  in  the  mow.  The  heat  is  produced  by 


226  Agricultural  Bacteriology. 

the  action  of  organisms,  such  as  the  molds,  the  same  as 
are  concerned  in  the  heating  of  manures.  Ear  corn, 
placed  in  the  crib  before  it  is  well  dried  may  likewise 
mold,  although  the  moisture  content  is  too  low  to  allow 
growth  of  bacteria.  Various  ground-feeds,  as  meal, 
readily  mold  if  kept  in  a  damp  place.  Wheat  becomes 
musty  when  damp.  All  of  these  troubles  are  caused  by 
the  presence  of  sufficient  moisture  to  allow  of  mold 
growth. 

The  preservation  of  many  foods  is  also  made  possible 
by  drying,  as  apples  and  other  fruits,  berries,  green  corn, 
etc.  Meat  is  also  protected  from  putrefaction  in  this 
way.  As  previously  stated,  the  muscles  of  a  healthy  ani- 
mal are  free  from  bacteria;  but  in  cutting  up  the  carcass 
the  meat  becomes  contaminated  with  bacteria  and  conse- 
quently undergoes  decomposition.  If,  however,  the 
meat  is  placed  in  a  dry  atmosphere,  the  outer  surface 
soon  becomes  so  dry  as  to  prevent  the  growth  of  bacteria, 
and  as  the  moist  inner  part  remains  free  from  organisms 
It  does  not  decompose.  If  the  drying  is  continued  until 
the  entire  piece  is  firm,  it  will  keep  for  an  indefinite 
period.  In  South  America  dried  meat  is  extensively  pre- 
pared and  is  shipped  to  all  parts  of  the  world.  When 
ground  and  mixed^  with  fat  it  is  a  very  concentrated 
form  of  food  and  is  used  where  fresh  meat  can  not  be 
procured. 

Dried  milk,  or  milk  powder,  and  dried  eggs  are  articles 
of  commerce  and  are  extensively  used  in  place  of  the 
fresh  materials,  especially  by  bakers. 

The  drying  of  foods  usually  injures  their  flavor  ma- 
terially, consequently  preservation  by  desiccation  is  be- 
ing replaced,  wherever  possible,  by  other  methods  that 
conserve  the  natural  flavor  to  a  greater  degree. 


Preservation  of  Foods.  227 

Salting.  If  certain  substances  like  salt  are  added  to 
organic  matter,  they  tend  to  preserve  it.  Most  kinds  of 
bacteria  are  unable  to  grow  in  a  saturated  solution  of 
common  salt.  This  fact  is  made  use  of  in  the  preserva- 
tion of  pork  and  corned  beef,  where  the  meat  is  placed  in 
a  strong  brine.  If  the  brine  is  too  weak,  certain  of  the 
bacteria  will  grow  and  the  meat  will  spoil.  Such  a  con- 
dition is  more  apt  to  obtain  during  warm,  than  during 
cold  weather.  The  effect  of  low  temperature,  which  has 
a  restraining  influence  on  bacterial  action,  together  with 
the  inhibitory  action  of  the  salt,  exert  a  more  pronounced 
preservative  effect  than  either  of  the  preservative  agents 
alone.  Salt  may  be  applied  in  a  dry  form  as  in  the  pres- 
ervation of  hides  and  meats. 

Smoking.  In  the  preservation  of  meats  such  as  hams 
and  bacon  by  smoking,  another  factor  is  operative.  In 
the  slow  combustion  of  wood,  antiseptic  compounds  be- 
longing to  the  cresote  group  are  formed.  These  are  de- 
posited on  the  surface  of  the  meat  and  are  absorbed,  and 
together  with  the  salt  protect  the  meat  from  the  action  of 
the  bacteria  on  its  surface^. 

Preservative  action  of  sugar.  Sugar,  although  fur- 
nishing an  ideal  food  medium  for  bacteria  and  molds, 
may  exert  a  preservative  action  such  as  is  shown  in  syr- 
ups. All  solutions  containing  sugar,  as  molasses,  cane 
and  maple  syrups,  or  fruits  conserved  in  sugar,  will  not 
keep  unless  they  are  sufficiently  concentrated.  "Where 
they  undergo  a  fermentative  change  they  are  said  to  have 
"worked."  The  preservative  action  of  sugar  in  concen- 
trated solutions  depends  upon  the  extraction  of  water 
from  the  bacterial  cells  causing  them  to  become  flaccid  or 
wilted.  Under  such  conditions  growth  can  no  longer 
go  on  and  fermentative  action  can  not  follow. 


228  Agricultural  Bacteriology. 

Sweetened  condensed  milk  is  an  illustration  of  this 
method  of  preservation.  Part  of  the  water  of  the  milk 
is  evaporated  by  heating  in  a  vacuum,  thereby  increasing 
the  density  of  the  milk.  The  addition  of  sugar  is  then 
made  which  still  further  increases  the  density  to  a  point 
where  bacterial  growth  is  impossible.  Such  milk  may 
contain  living  organisms.  Dilution  of  the  milk  with 
several  volumes  of  sterile  water  reduces  the  concentra- 
tion to  a  point  where  bacterial  growth  becomes  possible 
and  the  milk  then  undergoes  fermentation. 

Fruits  are  protected  from  decomposition  by  placing 
them  in  concentrated  sugar  solutions  in  the  making  of 
preserves.  In  the  preparation,  the  fruit  is  cooked  so 
slightly  in  the  sugar  that  it  is  not  rendered  sterile,  but 
the  bacteria  that  are  not  destroyed  ar^  unable  to  grow  in 
the  concentrated  medium.  Marmalades,  jams,  and  jel- 
lies owe  their  keeping  qualities  to  the  same  factors. 

Preservative  action  of  acids.  The  bacteria  are  un- 
able, as  a  rule,  to  grow  in  a  strongly  acid  medium.  This 
fact  is  made  use  of  in  the  preservation  of  many  foods  and 
even  fodders.  One  of  the  most  common  uses  of  acids  in 
the  preservation  of  foods  is  in  the  preparation  of  pickles 
with  the  use  of  vinegar,  which  is  itself  a  product  of  bac- 
terial action.  The  acid  reaction  of  the  vinegar  is  so 
strong  that  the  ordinary  bacteria  can  not  grow  in  it,  thus 
if  certain  vegetables,  as  cucumbers,  are  placed  in  the 
vinegar  they  will  be  protected  against  the  attacks  of  bac- 
teria. Some  of  the  molds  find  favorable  conditions  for 
growth  in  vinegar,  and  may  destroy  so  much  of  the  acid 
of  the  vinegar  as  to  allow  the  bacteria  present  to  grow 
with  the  result  that  the  pickles  are  spoiled.  Frequently 
spices  are  added  to  the  vinegar  to  be  used  for  pickles, 
since  they  improve  the  flavor.  They  also  have  a  preset 


Preservation  of  Foods.  229 

vative  effect  which  is  made  use  of  in  the  preparation  of 
such  foods  as  mince-meat,  sausage,  etc.  In  the  first,  the 
preservative  effect  is  aided  by  the  sugar  present  and  in 
the  case  of  sausage  by  the  salt. 

Fodders  such  as  corn,  clover,  and  other  leguminous 
plants  may  be  preserved  by  placing  them  under  such 
conditions  that  the  air  can  not  reach  them,  as  in  a  silo. 
In  such  cases  the  preservation  is  accomplished  by  virtue 
of  the  acid  which  is  formed  in  the  tissues  as  a  result  of 
the  continued  action  of  the  plant  cells  in  the  absence  of 
air. 

The  material  to  be  ensiled  must  have  the  plant  cells  in 
an  active  condition.  Silage  can  not  be  made  from  ripe 
or  frozen  corn.  In  the  ensiling  of  clover  it  is  necessary 
to  place  it  in  the  silo  before  much  wilting  of  the  plants 
has  occurred. 

The  living  plant  cells  continue  to  respire  after  they  are 
placed  in  the  silo.  The  supply  of  free  oxygen  is  soon 
exhausted  and  the  interspaces  filled  with  nitrogen  and 
the  carbon  dioxide  formed  by  the  respiring  plant  cells. 
The  cells  in  their  effort  to  keep  alive  draw  on  the  oxygen 
that  is  found  in  the  sugars  and  starches  of  their  contents. 
They  are  then  acting  exactly  as  the  anaerobic  bacteria 
when  they  obtain  their  supply  of  oxygen  from  the  sugar 
in  the  culture  medium.  In  the  effort  of  the  plant  cells 
to  obtain  oxygen  from  the  materials  of  the  cells,  they  de- 
compose the  sugar  with  the  formation  of  lactic  and  acetic 
acids  and  carbon  dioxide.  These  acids  are  formed  in 
such  amounts  as  to  prevent  all  bacterial  growth.  The 
silage  of  course  contains  many  bacteria  that  were  present 
on  the  fodder  ensiled,  which  continue  to  exist  in  the  si- 
lage but  are  unable  to  grow.  The  mold  spores  are  also 
present  in  the  silage  but  they  are  likewise  unable  to  grow 


230  Agricultural  Bacteriology. 

on  account  of  the  lack  of  free  oxygen.  The  carbon  diox- 
,ide  that  is  formed  in  the  silage  is  heavier  than  the  air 
and  does  not  pass  out  of  the  silage,  hence,  there  is  no  op- 
portunity for  the  oxygen  to  enter  from  the  surface.  It 
the  silo  is  not  perfectly  tight  at  the  bottom  and  on  the 
sides,  the  air  will  penetrate  for  some  distance,  and  allow 
the  molds  to  develop  and  cause  the  silage  to  spoil.  If 
the  silage  is  removed  from  the  silo  and  placed  in  a  loose 
pile,  the  molds  at  once  begin  to  grow  because  of  the  abun- 
dant supply  of  oxygen,  thus  furnished. 

The  plant  cells  in  their  respiration  produce  heat  just 
as  the  animal  does  in  its  breathing.  In  the  case  of  the 
living  plant,  the  heat  passes  off  as  rapidly  as  formed. 
In  the  mass  of  material  in  the  silo,  the  heat  produced 
can  not  be  radiated  as  rapidly  on  account  of  the  volume, 
hence,  the  temperature  of  the  silage  rises  to  120°  F.  or 
above.  This  high  temperature  is  retained  for  a  long 
time  and  prevents  the  freezing  of  the  silage,  a  very  for- 
tunate circumstance  without  which  it  would  be  very  diffi- 
cult to  use  this  method  of  preserving  fodder  in  the  north. 

If  the  plant  cells  are  dead  because  the  plant  is  ripe,  or 
because  of  being  frozen,  the  oxygen  of  the  air  in  the 
silage  is  not  used,  and  molds  are  able  to  grow.  Acids 
are  not  formed  by  the  decomposition  of  the  sugars  and 
consequently  various  kinds  of  bacteria  are  also  able  to 
grow.  The  result  is  a  rotten  mass  instead  of  a  fermented, 
but  succulent  and  nutritious  feed.  It  is  desirable  to  al- 
low the  corn  to  become  \vell  matured,  as  the  silage  formed 
is  not  as  acid  as  is  that  prepared  from  the  more  immature 
corn.  This  is  due  in  part  to  the  difference  in  the  compo- 
sition of  the  plant  at  different  stages.  If  the  corn  or  clo- 
ver is  somewhat  wilted,  the  cells  cannot  respire  even 
though  they  are  not  dead.  If  water  is  added  to  the  silage 


Preservation  of  Foods.  231 

as  it  is  placed  in  the  silo,  the  cells  are  revived  and  normal 
silage  is  formed,  when  without  the  addition  of  water  the 
silage  would  spoil. 

In  the  preparation  of  sauerkraut  the  fresh  tissue  is 
treated  in  very  much  the  same  way  as  is  that  placed  in  a 
silo,  except  that  salt  is  added  and  the  cabbage  is  packed 
until  the  interspaces  are  filled  with  liquid  instead  of  gases 
as  in  silage.  In  this  weak  brine,  acid-producing  bacteria 
grow,  apparently  forming  from  the  sugar  and  starches 
of  the  cabbage,  lactic  and  acetic  acids,  that  prevent  the 
growth  of  the  putrefactive  bacteria.  Sauerkraut  is  usu- 
ally stored  in  open  vessels.  On  the  surface  of  the  acid 
liquid,  molds  grow  which  gradually  neutralize  the  acid. 
At  last  a  point  is  reached  where  the  putrefactive  bacteria 
can  begin  to  grow.  The  sauerkraut  then  changes  into  an 
offensive  mass  of  decomposing  tissue. 

Preservation  by  canning.  In  many  of  the  processes 
of  food  preservation,  the  product  is  less  appetizing  than 
the  fresh  material.  In  order  to  avoid  this  as  far  as  pos- 
sible, the  process  of  preservation  by  canning  has  been 
introduced.  In  the  canning  of  most  materials  the  bac- 
teria are  absolutely  destroyed  by  heating  where  the  ex- 
posure is  made  either  at  the  boiling  point  of  water  for  a 
considerable  period  or  for  a  shorter  period  of  exposure  at 
higher  temperatures.  In  the  canning  of  corn,  peas, 
meats,  fish,  etc.,  the  latter  process  is  employed.  The- 
canned  foods  are  sterile  and  will  keep  for  an  indefinite 
period.  In  the  canning  of  very  acid  vegetables,  as  to- 
matoes, it  is  not  necessary  to  render  them  perfectly  free 
from  living  bacteria,  as  the  acid  prevents  germ  growth. 
If  the  heating  is  sufficient  to  kill  the  mold  spores,  yeasts, 
and  bacteria  that  do  not  form  spores,  the  tomatoes  will 
keep.  Some  bacterial  spores  will  be  left  but  they  can  not 


232  Agricultural  Bacteriology. 

germinate  on  account  of  the  acid  reaction  of  the  toma- 
toes. Corn,  peas  and  nonacid  vegetables  must  be  made 
absolutely  free  from  all  organisms.  This  is  often  quite 
a  difficult  process  in  the  household,  hence  these  are  han- 
dled with  less  success  than  are  the  acid  vegetables  like 
tomatoes. 

Preservation  by  cold.  In  the  modern  methods  of 
food  preservation,  low  temperatures  are  constantly  em- 
ployed. All  kinds  of  foods  are  placed  in  cold  storage. 
If  the  temperature  is  above  the  freezing  point  as  must 
be  used  with  certain  kinds  of  foods,  the  bacteria  grow 
slowly.  If  the  material  is  such  that  the  temperature  can 
be  reduced  below  the  freezing  point,  the  growth  of  bac- 
teria will  be  prevented.  Butter  and  meats  are  stored  at 
temperatures  far  below  the  freezing  point.  Eggs  and 
fruits  must  be  kept  above  freezing. 

Preservation  of  eggs.  Fresh  eggs  soon  deteriorate 
in  quality  due  to  the  growth  of  organisms  that  cause  the 
egg  to  spoil.  Infection  of  the  egg  may  occur  in  the  ovi- 
duct of  the  hen  before  the  shell  is  developed.  Also,  owing 
to  the  porous  nature  of  the  shell,  bacteria  may  work  their 
way  through  it  into  the  white  of  the  egg  which  affords 
them  an  excellent  food  medium.  A  number  of  methods 
have  been  devised  whereby  the  keeping  qualities  may  be 
enhanced.  These  methods  are  of  much  practical  value 
as  they  enable  the  surplus  eggs  of  summer  to  be  held  and 
disposed  of  at  more  profitable  prices  in  winter  when  fresh 
eggs  are  scarce. 

The  first  step  in  all  processes  of  preservation  should  be 
to  keep  the  eggs  clean  by  maintaining  clean  straw  or 
other  material  in  the  nests.  The  most  successful  way  of 
keeping  the  eggs  is  by  placing  them  in  a  solution  of  water 
glass  (sodium  silicate).  This  compound  can  be  procured 


Preservation  of  Foods.  233 

at  many  drug  stores.  It  costs  from  one  dollar  to  one  dol- 
lar and  a  quarter  per  gallon.  The  preserving  solution  is 
prepared  by  adding  to  nine  parts  of  water  that  has  been 
boiled  and  allowed  to  cool,  one  part  of  the  water  glass 
mixing  the  solution  thoroughly.  The  eggs  should  be 
placed  in  the  solution  within  twenty-four  hours  after  they 
are  laid.  It  is  claimed  that  April,  May  and  June  eggs 
keep  better  than  do  those  laid  later  in  the  summer.  It  is 
advisable  to  use  July  and  August  eggs  first  when  eggs 
from  all  of  the  months  have  been  preserved.  The  eggs 
should  be  examined  before  placing  them  in  the  solution 
to  see  that  they  are  clean  and  are  not  cracked.  The  stor- 
age room  should  not  be  above  60°  F.  and  should  be  as 
uniform  in  temperature  as  possible. 

Preparation  of  vinegar.  Fruit  juices,  as  apple  juice, 
undergo  a  spontaneous  fermentation.  There  are  present 
on  the  surface  of  the  fruit,  yeasts  which  find  favorable 
conditions  for  growth  in  the  juice.  These  change  the 
sugar  to  alcohol  as  in  the  preparation  of  cider  and  wine. 
If  these  liquids  are  allowed  to  stand  exposed  to  the  air, 
they  usually  undergo,  spontaneously,  what  is  known  as 
the  acetic  fermentation  in  which,  by  the  action  of  the 
acetic  acid  bacteria,  the  alcohol  is  changed  to  acetic  acid. 
The  bacteria  causing  this  change  are  aerobic  and  grow 
only  on  the  surface  of  the  liquid.  It  is  therefore  advisa- 
ble to  have  the  cask  only  partially  filled  with  the  liquid. 

The  acetic  bacteria  grow  most  rapidly  at  70°  F.  It  re- 
quires a  number  of  months  (12-18)  to  complete  the  proc- 
ess of  acetification.  The  process  may  be  hastened  some- 
what by  adding  to  the  cider  or  wine  a  quantity  of  mother- 
of- vinegar  which  is  simply  a  mass  of  acetic  acid  bacteria. 
After  the  process  is  completed  the  casks  of  vinegar  should 
be  completely  filled  and  stoppered  tightly  in  order  to  pre- 


234  Agricultural  Bacteriology. 

vent  the  growth  of  aerobic  bacteria  that  destroy  the  acetie 
acid  and  thus  weaken  the  vinegar. 

A  more  rapid  process  is  known  as  the  Orleans  process, 
in  which  dilute  solutions  of  alcohol  are  allowed  to  trickle 
over  beech  wood  shavings.  This  brings  the  liquid  in  inti- 
mate contact  with  the  air  and  after  the  shavings  once  be- 
come seeded  with  proper  bacterial  growth,  the  conversion 
of  the  alcohol  solution  to  acetic  acid  occurs  very  rapidly. 


CHAPTER  XXVI. 
BACTERIAL  DISEASES  OF  PLANTS. 

Bacteria,  as  a  rule,  grow  best  in  food  substances  that 
are  alkaline  in  reaction,  while  other  fungus  plants,  molds, 
rusts,  apd  mildews,  find  most  favorable  conditions  in  an= 
acid  medium.  The  juices  of  the  animal  body  are  alka- 
line, those  of  plants  are  usually  acid.  These  facts  have 
been  usually  regarded  as  the  explanation  of  the  greater 
susceptibility  of  plants  to  diseases  caused  by  fungi  other 
than  the  bacteria.  Very  few  important  diseases  of  ani- 
mals are  produced  by  molds,  and,  conversely,  few  bac- 
terial diseases  of  plants  are  of  great  economic  importance. 
Another  reason  for  the  greater  prevalence  of  bacterial 
diseases  in  animals  is  that  the  invasion  of  the  animal  body 
by  bacteria  is  made  possible  through  the  natural  openings 
of  the  body.  The  invasion  of  the  plant  tissue  is  more  dif- 
ficult since  there  are  no  natural  openings  comparable  to 
those  of  the  animal  body. 

The  diseases  of  plants  caused  by  rusts,  mildews,  smuts, 
etc.,  are  of  the  most  varied  nature  and  affect  all  kinds  of 
plants.  Methods  of  prevention  through  the  use  of  solu- 
tions applied  to  the  seed  as  in  the  treatment  of  oats  and 
barley  with  formaldehyde  or  hot  water  in  order  to  de- 
stroy the  smut  spores  on  the  grain,  or  the  spraying  of 
fruit  trees  to  destroy  the  fungi  thereon,  are  widely  and 
successfully  used. 

A  number  of  bacterial  diseases  of  plants  have  been 
studied.  The  knowledge  concerning  many  of  them  is 


236  Agricultural  Bacteriology. 

incomplete  and  methods  of  prevention  can,  therefore,  not 
be  so  successfully  used  as  in  the  case  of  diseases  caused 
by  other  fungi. 

Pear  blight.  A  disease  that  is  most  common  in  the 
pear  is  known  as  blight,  or  fire  blight,  since  the  diseased 
parts  appear  as  though  they  had  been  injured  by  fire. 
The  disease  affects  apple,  quince,  apricot,  and  plum 
trees.  It  is  said  to  affect  the  mountain  ash  and  several 
species  of  hawthorne.  The  bacteria  enter  the  tissue  most 


FIG.  23. — PEAR  BLIGHT. 

The  bacteria  causing  the  shriveling-  of  the  fruit  en- 
ter through,  the  blossom. 

often  through  the  blossom,  being  carried  from  flower  to 
flower  by  bees  and  other  insects.  They  may  also  enter 
through  wounds  on  any  part  of  the  tree.  The  bacteria 
grow  in  the  inner  bark,  gradually  working  their  way 
down  the  twig,  causing  the  leaves  to  turn  brown  and  to 
become  dry,  and  the  bark  to  blacken  and  shrivel.  The 
growth  may  extend  to  the  trunk  and  the  tree  be  de- 
stroyed. 

The  growth  of  the  bacteria  in  the  tree  is  most  rapid  in 
the  spring  and  summer  while  the  new  tissues  are  tender 


Bacterial  Diseases  of  Plants.  237 

and  full  of  sap.  By  midsummer  the  progress  of  the 
disease  is  checked  by  natural  causes.  The  bacteria  may 
pass  the  winter  in  the  affected  tree  and  with  the  advent 
of  warm  weather  begin  to  grow  once  more.  It  is  claimed 
that  trees  in  a  thrifty  condition  and  that  are  making  a 
large  amount  of  growth  are  more  susceptible  to  attacks 
than  trees  under  less  favorable  conditions. 

Prevention.  Since  the  bacteria  are  protected  by  the 
bark  nothing  can  be  done  to  destroy  them  by  the  use  of 
spraying  solutions.  The  only  method  of  preventing  the 
spread  in  the  tree  is  by  the  removal  of  all  affected 
branches  which  should  be  cut  off  several  inches  below  the 
last  visible  signs  of  disease  as  the  bacteria  extend  beyond 
this  point.  The  diseased  wood  should  be  burned,  other- 
wise the  bacteria  may  be  carried  to  still  healthy  trees  by 
insects.  Care  should  also  be  exercised  not  to  spread  the 
disease  through  the  pruning  or  grafting  knife. 

Cabbage  rot.  The  cruciferous  plants  as  cabbage, 
cauliflower,  turnips,  etc.,  are  subject  to  rots  caused  by 
bacteria.  The  most  common  method  of  infection  of  the 
plant  is  through  the  small  water  pores  on  the  edge  of  the 
leaf.  They  may  also  enter  through  wounds  such  as  are 
made  on  the  roots  at  the  time  of  transplanting.  It  has 
been  shown  that  the  seed  may  be  infected;  in  this  way 
the  soil  of  the  seed  bed  is  inoculated  with  the  bacteria 
and  opportunity  is  offered  for  infection  of  the  young 
plants.  The  bacteria  will  persist  in  the  soil  of  a  field  or 
seed  bed  for  a  number  of  years,  hence  it  is  advisable  not 
to  use  the  same^  field  or  bed  when  the  disease  has  ap- 
peared. Seed  may  be  rendered  free  from  the  cabbage  rot 
bacteria  by  soaking  it  in  a  one  to  one  thousand  solution 
of  corrosive  sublimate  for  fifteen  minutes. 

The  disease  appears  first  in  the  form  of  brown  spots  on 


238  Agricultural  Bacteriology. 

the  edges  of  the  leaves.  The  spread  of  the  disease  in  the 
plant  is  along  the  veins  and  ribs  to  the  main  stem.  On 
cutting  across  the  stem  of  an  infected  leaf  one  can  see 
the  blackened  ends  of  the  fibrous  strands  (fibro  vascular 
bundles).  The  channels  that  carry  the  food  and  water 
supply  of  the  leaf  are  destroyed ;  the  leaf  is  thus  deprived 
of  nourishment  and  dies. 

Efforts  to  combat  the  disease  in  the  field  by  the  re- 
moval of  diseased  leaves  have  proved  unsuccessful. 
Preventive  measures  must  be  confined  to  a  treatment  of 
the  seed  and  to  the  growing  of  cabbage  in  a  system  of  ro- 
tation rather  than  on  the  same  field  continuously. 

Melon  wilt.  Squash,  cucumber,  and  melon  vines  are 
subject  to  a  bacterial  disease  known  as  wilt  since  the  af- 
fected tissues  are  wilted,  due  to  the  plugging  of  the  water 
tubes  with  the  bacteria.  The  disease  is  most  prevalent  in 
the  early  summer  and  is  easily  told  from  all  other 
troubles  of  the  melon  family  by  the  sudden  wilting  of  the 
leaves  without  any  other  visible  symptoms. 

The  bacteria  live  in  the  soil  and  gain  entrance  to  the 
plant  through  wounds.  It  is  undoubtedly  spread  from 
plant  to  plant  by  means  of  the  various  insects  that  feed 
upon  the  vines.  The  only  means  of  prevention  is  to  grow 
melons  and  squash  in  rotation  with  other  crops. 


INDEX. 


Abortion,  contagious,  147. 

Acids,  preservation  of  foods 
by,  228. 

Acidity  produced  in  milk,  54. 

Actinomycosis,  142. 

Aeration  of  milk,  48. 

Aerobic  bacteria,  8. 

Air,  bacteria  in,  14;  contami- 
nation of  milk  from,  33. 

Alcoholic  fermentation  of  milk, 
60. 

Ammonification,  187. 

Anaerobic  bacteria,  8. 

Anthrax,  98;  spread  of,  103; 
vaccination  against,  101. 

Antiseptics,  12;  in  milk,  48. 

Antitoxin  for  tetanus,  132. 

Azotobacter,    205. 

Bacteria,  aid  in  animal  diges- 
tion, 208;  colonies  of,  18; 
determination  of  number 
of,  17;  distribution  of,  13; 
forms  of,  2;  in  soil,  174; 
nature  of,  1;  pure  culture 
of,  19;  reproduction  of,  3; 
size  of,  3;  structure  of,  2. 

Barn  air,  33. 

Bitter  milk,   61. 

Black  leg,  104. 

Butter,  65;  deterioration  of,  70; 
flavor  of,  65;  moldy,  72; 
sour-cream,  65 ;  sweet- 
cream,  65;  undesirable  fla- 
vor In,  71. 

'Cabbage  rot,  237. 

'Calcium,  182. 

•Canning,  preservation  of  foods 
-by,  J231. 


Carbon,  cycle  of,  181. 

Carbolic  acid,  168. 

Cellulose  digestion  of,  208. 

Certified   milk,    83. 

Cheese,  73;  Cafnembert,  80; 
Gorgonzola,  79;  Limburger, 
80;  ripening  of,  75;  Roque- 
fort, 79;  Stilton,  79;  Swiss, 
78;  types  of,  73. 

Chicago,  rules  for  production 
of  milk,  85. 

Chicken  cholera,  157. 

Cold,  effect  on  bacteria,  10; 
preservation  of  foods  by, 
232. 

Colored   milk,   62. 

Copper  sulphate,   169. 

Corn  stalk  disease,  109. 

Corrosive  sublimate,  169. 

Cows,  cleaning  of,  28;  clipping 
of,  28;  tuberculosis  of,  39. 

Cow  pox,  146. 

Cow  stalls,  27. 

Cream,  ripening  of,   66,  69. 

Cresol,   168. 

Culture,    media,    15. 

Denitrification,  190. 

Diphtheria,  bacteria  of  in  milk, 
40;  of  fowls,  159. 

Dirt  in  milk,  26. 
Disinfectants,  12. 
Disinfection,  165. 
Distemper  of  dogs,  163;  of 

horses,  163. 
Drying,    preservation    of   foods 

by,   225. 

Eggs,  preservation  of,  232. 


240 


Index. 


Factory  by-products,  31. 

Farcy,    129. 

Farm  separators,  31. 

Feed,  effect  of  on  bacteria  in 
milk,  34. 

Ferrous  sulphate,   169. 

Fermentation  of  milk,  53. 

Fire  blight,   236. 

Foods,  preservation  of,  225; 
preservation  of  by  drying, 
225;  preservation  of  by 
salting,  227. 

Foot  and  mouth  disease,  162. 

Foot  rot  of  sheep,  162. 

Fore  milk,  25. 

Formaldehyde,  169. 

Fowl,  cholera  of,  157;  diseases 
of,  157;  roup  of,  159;  tu- 
berculosis of,  126;  typhoid, 
159. 

Fungi,  1. 

Immunity,  natural,  95;  artifi- 
cial, 95,  102. 

Intestines,  bacteria  in,  14. 

Intestinal  diseases,  caused  by 
milk,  42. 

Garget,    144. 
Germicides,  12. 

Glanders,  127;  diagnosis  of, 
130. 

Gorgonzola  cheese,  79. 

Heat,  effect  on  bacteria,  11. 

Hemorrhagic   septicemia,    107. 

Hog  cholera,  151;  prevention 
of,  154. 

Hogs,  diseases  of,  151;  tuber- 
culosis of,  125. 

Horses,  distemper  of,  163. 

Hydrophobia,  136. 

Lactic  acid  bacteria,  54. 
Leguminous  plants,  198. 
Lesions  of  disease,  96. 
Life   in    soil,    177. 
Limburger  cheese,  80. 
Lime,  167. 
Lumpy  jaw,  142. 


Mallein   test,   130. 

Mammitis,  144. 

Manures,  bacteria  in,  207;  de- 
composition of,  209;  fire 
fanging  of,  211;  losses 
from,  210;  in  milk,  26. 

Market  milk,  82. 

Mastitis,  144. 

Melon  wilt,  238. 

Microscope,  20. 

Milk,  abnormal  fermentation 
of,  57;  aeration  of,  48;  al- 
coholic fermentation  of,  60; 
bacteria  in,  90;  bitter,  61; 
care  of,  89;  certified,  83; 
clarifying  of,  46;  colored, 
62;  commissions,  83;  con- 
densed, 52;  contamination 
of,  23;  cooling  of,  46;  dis- 
ease-producing bacteria  in, 
38;  filtering  of,  45;  gassy 
fermentation  of,  56;  house, 
37;  market,  82;  pails,  28; 
pasteurization  of,  49;  poi- 
soned, 43;  preservation  of, 
44;  slimy,  58;  souring  of, 
53;  straining  of,  44;  tuber- 
cle bacteria  in,  39;  utensils, 
contamination  from,  29; 
utensils,  washing  of,  32. 

Milker,  contamination  of  milk 
from,  34. 

Milking,   88. 

Minerals,  action  of  bacteria  on, 
182. 

Nitrification,  187;  conditions 
favoring,  188. 

Nitrogen,  conservation  of,  192; 
fixation  of,  196,  204. 

Nodular  disease,  126. 

Nodules  on  legumes,  199. 

Odors,  absorption  by  butter,  72; 

by  milk,  36. 
Organic  matter,  decomposition 

of,  178. 

Parasitic  bacteria,  7. 
Pasteurization,  49,  87;  of  cream,. 


Index. 


241 


Pathogenic  bacteria,  spread  of, 

95. 

Pear  blight,  236. 
Period  of  incubation,  96. 
Pickles,   228. 
Phosphorous,  182. 
Plants,    bacterial    diseases    of, 

235;  leguminous,  198. 
Plant  food,   171. 
Poll  evil,  162. 
Potassium,  185. 
Preservatives.  12. 

Rabies,  134;  diagnosis  of,  139; 
prevention  of,  138;  symp- 
toms, 135. 

Roquefort  cheese,  79. 

Roup,   159. 

Salting  foods,   227. 

Saprophytic  bacteria,  6. 

Septic  tank,  220. 

Septicemia,  107. 

Sewage,  disposal,  219;  purifica- 
tion, 219. 

Silage,   229. 

Slimy  milk,  58. 

Soil,  bacteria  in,  13,  174;  inocu- 
lation of,  202. 

Spores,   5,   58. 

Stable,  disinfection  of,  169. 
.Starters,  home-made,  66;  pure- 
culture,  68. 

Sterilization,  16. 


Stilton  cheese,   79. 

Sugar,    preservation    of    foods 

by,  227. 
Sulphur,    185. 

Sweet  curdling  of  milk,  57. 
Swine  plague,   156. 
Swiss  cheese,  78. 
Symptomatic  anthrax,  104. 

Temperature,  of  cows,  120;  ef- 
fect on  bacterial  growth,  9. 

Tetanus,  131. 

Transmissible   diseases,   88,   92. 

Tuberculosis,  86,  110;  diagnosis 
of,  118;  distribution  of, 
110;  of  fowls,  126;  of  hogs, 
125;  symptoms  of,  117. 

Tuberculin  test,   118. 

Typhoid  fever,  bacteria  of  in 
milk,  40;  of  fowls,  159. 

Udder,    contamination   of   milk 

from,  24. 
Utensils,  milk,  89. 

Vinegar,   233. 

Water,  90;  bacteria  in,  13;  dis- 
ease-producing bacteria  in, 
215. 

Water  glass,   232. 

White  scours,   161. 

Wisconsin  curd  test,  63. 

Yeasts,  60. 


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